Tests Round 1
Test 1: Renaming the name as B5BE on decchi, and keeping the name in the list in ENG Pearl to B5BE didn't work.
Test 2: Keeping the name B5BJ on decchi, and renaming the name in the list in ENG Pearl to B5BJ didn't work.
Test 3: Renaming the name to B5BE on decchi, and renaming the name in the list of JPN Pearl to B5BE works.
There probably is some kind region tracking, but I can't tell if it's decchi or DPPtHGSS being the side that has the region byte that is being verified.
Interestingly enough, I can't seem to find the list in HGSS.
Tests Round 2
Replacing all bytes that contain 0x01 to 0x02 between offsets 0xC0 to the end, did not make it not receivable on JPN games. (The idea was to accidentally replace a JPN language byte with ENG, but that didn't work)
Maybe what controls it is the script in decchi (script for the wonder card transfer), as opposed to a language byte being checked.