Due to how stores & streaming services pay, it wouldn't be possible for multiple DistroKid users to upload music using the same ISRC. That's because stores payout by ISRC, and therefore if more than one user had a song with the same ISRC, DistroKid wouldn't know who to pay. And the second usage might not even be authorized (i.e. you wouldn't want some random person using your ISRC)
However, we have good news!
DistroKid is one of the only distributors that makes it easy to route all (or any amount of) earnings from any track, to any other DistroKid member(s).
So if you're moving or transferring ownership of a release from one person to another, simply use DistroKid's "Teams" feature to redirect 100% (or any percent of) earnings from the chosen track(s), to the new DistroKid account.
This will ensure that all metadata, including ISRC, remain intact and unchanged. Another added bonus is that your stats and playlist positions should remain intact.