Look closely at the specific wording of the law. (and no, I don't know exactly what it says)
IF the words "permanent" are in there, that one thing, if the law is worded something like "containing over" or "capacity above" that's another.
Shotgun round limits (3 rnds) don't require anything permanent, as long as you cannot put more rounds in the gun than allowed (in the field) that meets the law. A piece of wood in the mag tube suffices.
Of course, that's a game law...
it seems that LEO look a bit suspiciously upon a follower change,...
Do they? are you guys in CA being inspected by LEOs? Are there compliance checks? And has anyone been arrested and charged because of the LEO's suspicions?? Is there a written standard for what is and is not an acceptable method of permanently altering a magazine? Or is it left up to the whim of the administration of each jurisdiction?
Last year, WA passed (barely) a law requiring a background check for all transfers. That law is so poorly written that state agencies, including the State Patrol are refusing to enforce it, UNTIL the state provides them with a written standard for what is, and is not a transfer covered under the law. Which, to date (as far as I know) the state has not done.
If there's no written standard in the law, saying A is legal and B is not, LEOs can look suspiciously at you all day long, but they can't legally do anything about it.
IF there is no standard, then some poor fellow will eventually become the test case. After that, there will be a standard, and you'll have to live with whatever it is.