this doesn't support editing the rear side of a sign, since the 1.12 format doesn't allow us to represent the rear text, and it would necessitate API breaks to support anyway.
However, we can quite trivially support APIs for the sign GUI, which plugins can use to enable editing signs. PocketMine-MP doesn't currently permit this, since it's currently an experimental feature in 1.20, but plugins can simply use Player->openSignEditor() to mimic it.
This is, however, a byproduct of the fact that APIs needed to be added in order to facilitate the use of OpenSignPacket in 1.19.80.
in pretty much every case, these usages really wanted to read the tag's contents anyway, which can be combined with a getTag() and instanceof call for more concise and static analysis friendly code.
In the few cases where the tag contents wasn't needed, it still wanted to check the type, which, again, can be done in a more static analysis friendly way by just using getTag() and instanceof.
