No, you won't hurt the plants. You really should wait until it's not so mucky out there, though, to avoid compacting the soil. Don't know about where you area but there's been a lot of snow fall/melt where I am and the ground is saturated, no way would I work in the beds right now, it's too wet. Anytime it's dry enough though - go for it.

it will most likely come back unless you're too nice to it. Keep it dryer than usual because it doesn't have any leaves. Keep it in a warm place and expect it might take 4-6 weeks before it actually starts growing actively again. They seem to have a delay time before they start growing again after they're frosted, like they're waiting to make sure that the weather has really changed.

Kris, I think you are missing the point. With few exceptions there is no valid reason why most Miscanthus cultivars CANNOT be cut back in fall. A good many are hardy to zone 4, the vast majority to zone 5 and few more tender cultivars to zone 6. With the exception of the slightly more tender condensatus cultivars, they are root hardy to at least -20F, some to -30F. It is highly unlikely leaving the dead stalks through winter will significantly increase winter hardiness except in very marginally hardy cases. Cutting back in spring for most OG's is only an option, not a requirement. I am also a bit confused about a couple of other statements you made. "the majority of the public only grows Miscanthus". That's a pretty broad statement and unlikely to be supported by fact. In a number of southwestern states, including Kentucky, Miscanthus sinensis and many of its cultivars are considered invasive and not recommended to be grown. And you are ignoring the popularity of scores of other grass species - Calamagrostis, Panicums, Pennisetums, Deschampsia, Stipas and all the native prairie grasses and sedges that are so popular, not to mention bamboos and all the grass-like plants commonly grouped as OG's, like liriope and mondo grass. Gardeners are a diverse bunch and live and garden in diverse conditions and making blanket statements such as this is innaccurate and misleading. Miscanthus is not easily damaged by cold except in areas of borderline hardiness, like most other plants. While I currently live and garden in zone 8, I have also gardened in colder climes and cutting back most miscanthus in zone 5 (eastern WA) in fall or early winter never compromised the health of the plants I grew there. I would look to other reasons why your miscanthus are not doing well if cut back in fall or early winter as opposed to spring. And finally I think you are confusing aesthetic concerns with cultural requirements. Cutting back dead top growth of any herbaceous plant can be done at any time. There is some slight benefit afforded by leaving dead plant material intact over the winter but only an increase of a few degrees of protection, far less than what would be accomplished by mulching or by the insulating factor of snow. Certainly not a concern when the plant in question is hardy to a zone or two or more lower than your current location. And in areas where miscanthus is invasive, it makes very good sense to cut the grasses back early so that the seed is not dispersed by winter winds. As for my responsibilities as a professional in the green industry, I am well aware of them. And the dispersal of accurate information is paramount among them. And if I were you, I'd be a bit more concerned about your responsibilities as a green industry professional in encouraging the planting and spread of potentially invasive plants in your area. Here is a link that might be useful: Kentucky - invasive species

I'm no peony expert, and I've heard to wait until the first hard frost, too - but I don't think it would HARM the plant any if you cut back a couple of weeks or so before the hard frost. The idea is to keep the green leaves on the plant as long as possible because thru them the plant gets nutrition to the root to store up energy to produce blooms. So cutting back foliage a few weeks earlier would theoretically reduce that energy storage a wee bit. I don't know if anyone's studied that to see if a few weeks actually makes any discernable difference. Maybe lose 1 bloom out of 20?