Looks like a bigger change. I think it should rather go in after the v2.6 release.
What an unfortunate timing. The mentioned situations which this patch aims to fix are definitely very noticeable and I'm sure a lot of Atari devs would appreciate a new release with this feature in (as opposed to waiting another year for 2.7...).
Personally I build Hatari from sources but I'm sure many people don't (esp. when on Windows).
The patch seems quite local, maybe it's worth the risk? And there's still 2.6.1 possible. Just my two cents.