Yes, I think you can start pruning now, especially if your autumn flush of flowers has finished, I've pruned and replanted all mine. On Marilyn Munro in Perth, sorry can't help you there but I know it's a hardy rose, one of Swains, I believe, I've bought lots from them over the years and found their plants always strong and reliable, Swains are a large, reputable NSW rose breeder and nursery.

Hi Clare
I usually leave the pruning till the middle/end of July. A lot of my roses are still flowering, although the bushes are looking a bit straggly. We have had quite a bit of cold, wet weather in the last week or two, so that hasn't helped the bushes and like you I am itching to get out there and tidy up a bit, but I must be patient, I must be patient, I must be patient....
I'm sorry, I don't know anything about MM

Yep,
I must be patient too .I've been looking around the neighbourhood and no one started just yet .Thx.

Treloar at Portland has MM and so has Johns World can't help with Perth unfortunately
Leyla

Don't Perth , Melbourne etc. prune in June ? Toowoomba prunes now. Hotter areas like here in Brisbane prune in July.

Couldn't wait. Pruned my roses this morning, 2nd July, got busy weekends for the rest of the month so this was my time.

Planted 4 newbies (grand total of 22 roses now) , Black Magic, Perfect Moment, Ian Thorpe and Tequila Sunrise. Anyone growing these fellas ?

I pruned mine (in Perth Northern Suburbs) three weeks ago while hubby was home to empty the trailer!
It is the earliest I've done them. I gave them a spray and just this week noticed all new healthy growth coming out. They look really great so I'm hoping my necessity to be early is a good thing.
I also pruned particulary hard this year and took out growth that I wasn't happy with.
Will keep you posted