I want to speedrun halo: combat evolved through halo: the master chief collection, Is this alright or should I just get the game separately. thanks

You'd want to ask the game's community. They'll probably have rules regarding that.

You definitely won't get banned for it.  The game's community probably has separate categories for that.  If it doesn't, maybe you'll be the first.

this being said if you are interested in speedrunning the halo series, you will want to go to haloruns.com, as the halo speedrunning community runs its own site as opposed to using this one (Hence why only category extensions and co-op runs are on this site).