I don't know what your script does and if it needs fixing for 2026.3. What I said is that we usually put a lot of effort into keeping our ABIs and APIs stable, as exemplified with the 2026.3.1 hotfix where we fixed an issue with the UV tag interface that made it incompatible with old code.
2026.3 contained the UV manager overhaul as its main feature. We tried not to break any glass there but I cannot rule it out. when you find a regression in our APIs, you can also always report it. when the break was unintentional we usually provide a fix (in critical cases even a hotfix) or at least a workaround.
We also usually do not remove systems. For example, the old content system and its "Content Browser" is still in our APIs and Cinema, although it long has been replaced by the Asset Browser and API. Can I guarantee that the UVPeeler will not be removed soon? No, we sometimes have to remove things. But it is quite rare.