Computer slowdown / Too many tracks / Bouncing down help

I'm trying to use the bouncing-down technique and it was working okay... until:

1. I suspect my bounce-downs sound different from the master tracks. Not sure yet, but I swear they lack a little oomph.

2. This is probably a Reason only problem, but I'm working on a middle section of a track where a tempo shift occurs. I exported the whole track and started working on some guitar sections. After hours of honing these, I bounced the guitar tracks down and put them back into the master section only to find that Reason is altering the tempo of my guitar tracks when the tempo shift occurs. This is unwanted because I naturally slowed down my playing during the recording phase, so they're being slowed down twice and going out of sync with the track. This happens even when I disable stretch.

3. This is a general issue: I find if I'm working on a separate section to be bounced up to the main mix, I'll encounter moments where playing (e.g. guitars) means I want to alter something like the physical layout of the main track (such as a rhythm section). This is where it starts getting messy because I end up with several different sections in various states of progression. I start losing track of what's going on and tying myself in knots. I guess this can't be helped and it's about maintaining a very rigorous workflow.

Most DAWs have a freeze track function that temporarily renders a track as audio within the song, cutting down on processor strain. It looks like Reason doesn't have this, which is strange.

no, i don't think it does this. you're right, it's a bit of an oversight. i guess propellerhead are confident in it being such a compact, all-in-one DAW that it's not necessary.

I think you're probably right when you say it's about maintaining a rigorous workflow. I also work with a slow/buggy computer (with Reason, which I've always found to be exceptionally solid) and consequently I don't even turn the bitch on until the song is essentially "written". Also, I try to mimic the method that seemed to work quite well waaaay back in the day when, as a rule, they seemingly always had different people to a. write the song, b. arrange the song, and c. perform the song. I do sometimes simply open up Reason and fuck around but that gets boring as my main thing has always been about the live & visceral aspect of music and not so much with the twiddling & tweaking of knobs.