Questions regarding achievements #21 & #26

[GoatLoverX]

If I prestige or ascend even once, will I never
be able to get those achievements without resetting my save?

[lordoftheabeliangroups]

No.

"Without doing X" generally means "without doing X since doing the last thing that resets X". So "without prestiging" means "without prestiging since your last promotion, infinity, eternity, unity, or whatever comes after that".

[spidweb01]

Don't turn achievements into challenges. If it seems hard to do, then don't waste time on it. Keep progressing and you'll be able to do them practically instantly at some point. I think #029 is really the only one that may take some time, but still can be done quickly (less than 5 minutes). They don't have to be done in your first run or even your first Eternity.

[Kyouko Tsukino]

If it looks like you will take a very long time to do any of the achievements, it means you're not ready for it yet, or your automation needs corrections.

Only time achievements would be easy (or "easier") would be if you're ready for them, or if you've overshot them. They're not in a random order, they (mostly) follow progression.