There will be time travel. He was seen in the premier of Legends of Tomorrow which to me means that the team will have to ask the Flash for his help once they know RF is around.
As to not changing the past, well when Barry goes back and fixes a day as he has done, that is one thing. But at the end of season 2 he went back 15 years.
Changing the past at all is a bad idea, usually, but changing 24 hours will not have as major an impact as changing 15 years.
RF seems to be more poweful ths time around..
As his survival made him a kind of paradox, almost like a Time trapper lite then, as his goofing around with barry reminds me of when the TT "played" and made the pocket Universe SB!