The Block Hooks API (WP 6.4+) lets a block declare it should auto-insert relative to another block. blockHooks in block.json maps target block names to positions (before, after, firstChild, lastChild).
This is the right way to add a ‘powered by’ block after every footer template part, or to extend a third-party theme without forking it.
Hooks fire at insert time, not on render — the user sees the resulting block in the editor and can remove it.