First, OP, I think you shouldn’t stress out about getting a 4.0. There’s not a whole lot of difference between a 3.9 and a 4.0 when it comes to transferring.
Second, most professors are really annoyed when you go to them asking for extra credit or to round up. It’s true that some professors do offer extra credit, but they usually do it a priori, and often something relevant to the class (like the research projects). However, many more professors would be sympathetic to a request if you explain (AHEAD of time) that you’re asking because your group members are slackers and you’re afraid your group project grade is going to be lower than your potential. Although professors do love to assign these group projects, they do understand that group projects often mean an overachiever is stuck in a group with people without his work ethic.
Yes, professors do sometimes change the grading scheme partway through the class and do often round up. However, when it’s been done in my experience, it’s because the professor has noticed a class-wide pattern in the grades (e.g., the midterm grades were really low because the professor included a unit she forgot to teach or didn’t teach well, so she gives people the option to drop the grade and only count the final). A professor is unlikely to change the scheme so that one student with a B can get an A.
One class I TAed for, the professor had a concept he called Mercy. If the student was borderline close to the next level of a grade, and the student had exhibited top-level behaviors (excellent attendance, asking questions, coming to office hours) the professor would bump their grade to the next level. (It was actually labeled “MERCY” in the spreadsheet, lmao!). Another class I co-taught, a student earned a B-, and the professor asked me to bump it to a B because she wanted everyone to get a B or higher in the class. (And even the B- was “mercy” on MY part - I really wanted to give her a C.) However, asking professors for this kind of bump seems to irritate them rather than get what you want. (One of the reasons is that college students tend to brag about this stuff. If they cave to you because you ask, and you tell 10 of your friends, then they all ask when they get borderline grades. You get a reputation as the professor who adjusts grades if someone just asks nicely. And it rolls down the hill. And what’s borderline? 89.2 is certainly close to a 90, if that’s an A, but what about that kid who gets an 88.9? If you bump him too, then the one who has an 88.2 is going to try it too.)
If you approach the professor, I would make it less about asking for special consideration and more about expressing concern about your group project. Then you can slip in there that you have a 4.0 you’d like to maintain (casually, not making it the focus). See how the professor reacts. Personally, if I had an otherwise excellent student who made one mistake and who was super close to an A, and told me they had a 4.0, and it was their super slacker group mates that were keeping them away from the A (and I had reason to believe they were telling the truth based upon those slackers’ performance in the class), I’d maybe try to help them out with some mercy if they were close enough to make it feasible. (I tend to think of that as one point or less away from an A. 89.1 okay; 88.5, no dice.) However, I wouldn’t tell them I was doing it. I’d say “I’ll take that into consideration for the final grades.”