I wouldn't do it! If I recall correctly, you'd be altering the soil structure and not in a good way. I know the urge to get going out in the gardens as soon as possible, but this rain is typical of April, and IMO you need to wait until it's drier out there.

This spring with its copious rain has wreaked havoc here for me -- the poor drainage in the driveway has created all five of the Great Lakes which reappear every time it rains. Like right now... AND the extremely high water table that we have out in the back gardens resembled the Pacific Ocean for over a week -- plus that water has now decided to come into the finished basement in four different rooms. Two nights ago, we were using a submersible pump and a big ShopVac to deal with it from 2.00AM until 6.00, at which point I gave up and went to bed for a couple hours. Up again for the remainder of the day. Such fun!!

Major heavy rain right now again, for the rest of this night. Guess what I'll be doing!

Digging now will just make these incredibly hard dirt clods that are very difficult to break up. Wait until things dry out.

I've never found a rototiller to be much good for anything. Even a big one can barely get below the sod, and rocks and roots are insurmountable obstacles.

Peat is a terrible amendment unless you are growing swamp azaleas in a fen. If it ever dries out, it is a bear to rewet, and the plants will dehydrate until that happens. What you need is compost, manure, shredded leaves, etc.

Never till wet soil, it damages soil structure. Tilling in turf grasses is likely to be followed by an extended period of re-sprouting from fragments. Regarding amendments it depends on what you are planning to grow. And even for vegetable plantings you don't want to load up the soil with amendments.

The Myth of Soil Amendments, Part III
“Healthy soil has high organic content”

https://s3.wp.wsu.edu/uploads/sites/403/2015/03/soil-amendments-3.pdf

thanks all! good to know.
I'm very fortunate in that the rototiller worked last year in a nearby space, so that gives me hope lol.

As far as what I'm growing it'll be mostly some small perennials as well as roses. No vegetables :)
I got a small amount of peat moss to add for the roses, I've heard it's good for the roses and have had decent results using it before (or at least not negative ones). Is adding it not the right call? (if it matters I'm not adding a whole lot of it)

Loosen existing soil and plant roses and perennials in that, mulching afterward to introduce the benefits of organic material to the site without amending - see at above link for problems with amending long term plantings.

Garden centers are first and foremost retailers, have therefore in the past promoted the erroneous practice of the amending of planting holes for long-lived plants because it generates what have been called "tie-in sales" - send you home with a bag of soil amendment and they have added to your purchase total.

Maybe you better get some fertilizer too, and so on.

The Myth of Indisputable Information
“Nursery brochures are always the best sources of appropriate planting practices”

https://s3.wp.wsu.edu/uploads/sites/403/2015/03/planting-instructions.pdf

I've been dodging rain drops to try to get some digging done too, and what I finally thought of doing, was to cover the area I need to dig with plastic so when I had the time to dig it, it was ready and not too wet. That has worked out well. We have big enough plastic pieces that we had from painting drop cloths and for a couple of small areas, we used black plastic garbage bags overlapping. Try that.

I have clay/loam soil and it's got a nice structure and holds water but not too much, so the last thing I want to do is give myself a problem ruining the soil structure.

For my roses, I was lucky - I had 3 new bare root roses delivered in early April and it was dry enough to dig them in within a few days of arrival. For the roses that were already in the bed, they've started leafing out, looking very good and all I add every season around the base, is a layer of compost and some alfalfa meal. I just use a hand 'claw' and gently work it into the top inch or so and pull the mulch back over it. That's all I do every year, then I repeat the same treatment after the first flush of bloom to prepare for the next flush of bloom. I also use organic fish emulsion/seaweed fertilizer - liquid - either according to the directions or half strength every time I water. I feel I've had very good results with this routine.

excellent suggestion prairiemoon!

shockingly we are supposed to get 3 days of no rain (no sun either but beggars cant be choosers). But knowing new england, if/when the weather changes back to rain I'll be putting plastic down. That sounds like a good routine for your roses, mine are just waking up now. Unfortunately I lost a few this winter. 1 got crushed by a fallen tree branch but seems to have one teeny little cane re-emerging (like for real this branch smashed it in half and landed right in the center and broke all the canes). But I have 1 or 2 that are looking iffy, and I think 4 that flat out died. I'm still going to give it a few weeks before I rip anything out. But the ones that died I think 2 of them are actually my fault, I think I applied too much acidifier near them and that they scorched. Time will tell! Silver lining - if those roses do die it will leave room for either some evergreens I wanted to add for fall color, or for my lilac bush that has been squatting in a container.

Embothrium - thank you for the read! it certainly helps to get more background knowledge. It's crazy, I try to keep up on what I can however there's so much, and the more I learn the more I realize there's even more to learn haha.