Photos and a plan will get you a lot more answers

Customization needs to occur in the design phase. Rebuilding it later will be 5x as expensive to do.

Added photos for the one to be installed and the desired microwave. To customize now with the builder would put a stop to our building process and is not an option.

Contact the manufacturer NOW and find out if you can order additional cabinets. Hopefully the builder will refer you to their supplier. Worse case you rip out the island and replace all three cabinets with something really similar from a different manufacturer.

The island will have a lovely quartz countertop. Is it not possible to rebuild the insides to accomodate pull out drawers leaving the shell including the quartz untouched?

It would require more skilled work to reconfigure the cabinet. If the quartz is not on it yet I'd change the cabinet now. You can put cookbooks or a basket of potatoes(?) in the cavity for now.

If you don't put in the electrical connections now for the microwave, you won't be able to add it later without tearing out the island. So if you want a microwave, design it to include the microwave now, and have your electrician put in the correct wiring/outlets.

You can’t effectively rebuild cabinets the way you are describing, it will be cheaper and faster to pull the tops and drop it on three new cabinets. As noted you need to address the electrical now. Assuming you can get the electrical addressed by the builder the cabinets can be swapped out whenever they arrive pretty readily.

The island will be wired with an outlet on each end. Will this be sufficient to tie into for the microwave install?

@nwheidi no, it's not sufficient. You'll need the correct appliance outlet for the microwave in the location in which it will be plugged in.

Microwaves require a dedicated circuit if permanently installed

Is this something an electritian can add after the island is installed? Just trying to find ways to adapt the stock island plan.

You need 2 circuits pulled to the island, NOW, before its built. And then the cabinets need to be designed to have the room for the electrical workboxes on the ends and for workbox for the MW, in the spot the manufacturer inficates. They take up room, and you may need deepwr cabinets to have that room. It’s Tetris. And you cant go back and do any of this later without it costing way way more.

As I said in my original comment, you can certainly add electrical after the fact, but it will require taking apart the island. Much easier to plan for it now.

Well that just sucks! The builder will require me to apply for change orders and said it will delay my build and stop everything. We are almost finished framing, roofing next week. We are up against weather deadlines to get dried in before bad weather stops build. My options look bleak.

Find out what the change order will cost. It probably won't be more than having to re-do the island later. In fact it might be less.

What I just don't get is the island in question consists of 3-27" base cabinets. Why is it so difficult to just switch out one of these with a microwave ready 27" base cabinet. Obviously I'm not a contractor or builder just an average home owner but it seems like this shouldn't be so difficult. It's not a question of change order costs it's that they will put a hold on my build while they sort out all the paperwork to switch this out. Dealing with a mass builder so I'm limited as to what I can do and everything they do takes so long.

Are these custom or stock cabinets? Your cabinet line may not offer a 27" microwave base cabinet.

Are you on a slab or raised foundation? If slab adding a circuit means a jackhammer... If this is something you want plan for it now, at least the electrical portion. The electrician can easily add a circuit now and terminate it under the island in a junction box so you can replace the cabinets whenever.

Raised foundation, thanks I'll make sure an electrician adds that now. Seems like a handyman or contractor could adapt a 27" stock base cabinet to fit the 24" drawer style microwave or maybe the microwave has an install box that can be purchased to retrofit into stock cabinets.

You also said you wanted the other cabinets to be converted to drawers. Where does the drawer or drawer face below the microwave come from? Yes a custom millshop can make the change or you could just plan for that now.

Well the microwave is the most important and now I will just focus on that and insert drawer style pull outs into the cabinets instead of trying to replace those too. Imagine I'd have to have someone build those two cabinet doors under the microwave.

To answer your question, the most difficult thing about adapting it later is the paint match. There are several methods to adapt it later, that will work and are easy enough for a decent finish carpenter or cabinet installer but you will need to order some parts in corresponding paint to do it.

The easiest way is to order three matching drawers fronts, one of which is about 18" - 18.75" tall. That drawer front can then be cutout and permanently mounted. The microwave will then set inside that drawer front giving the illusion of intention.

Another option is to order extra filler strips that are paint matched and then another drawer to the bottom. The Sharp microwave opening is 15.75" tall. Your cabinet is likely 30.5" tall plus a 4" toe kick. The actual drawer front size you would need to order depends on the overlay.

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Your much better option is to replace the center cabinet later with a new cabinet.. Go separately to the cabinet place and order a 24" microwave ready cabinet and two filler pieces. A cabinet installer can then unattached the top, persuade the middle cabinet out, install the new cabinet, add filler strips and reattach the top. You want someone bonded, insured and experienced doing it but it isn't hard.