As you already stated, it is debatable. The problem with permanent is many, many things are not as permanent as the government claims they are.
If the permanency of a pop rivet is debatable, so is the permanency of a mag block. Without an example of the legally considered minimum for "permanent" we literally have nothing to go on but our feelings based on Fear, Uncertainty, and Doubt. The next best thing we have to go on is "what would a reasonable person consider permanent?". That's a loaded question as there are plenty of reasonable people out there that don't even know magazines can be disassembled and through their ignorance may decide "I can't put 10 rounds in it, so... it must not be an LCM".
How about an epoxied on floor plate? You can just cut it off, take out any limiting devices, reassemble, and glue it back together.
What if you put a blind roll pin in the floor plate so it can't be removed? Drill it out.
What if you epoxy a block to the floor plate that keeps you from both removing the floor plate AND putting in more than 10 rounds? Cut off the floor plate and block in one fell swoop and epoxy the floor plate back onto the mag body.
What if you epoxy a limiter to the bottom of the follower AND roll pin the floor plate AND epoxy the floor plate so it can't be removed? Surely that's permanent? Unless you cut off the floor plate, cut off the limiter from the follower, reassemble, and epoxy the floor plate back on.
What about a 10 round spring and a floor plate that fills the empty void? You can just cut off the floor plate, punch out the piece that fills the void, replace the spring with a 30 round spring, and glue the floor plate back on?
How about a 10 round mag body on a floor plate that mimics the bottom half of a 30 round mag? I can't see any way to 'convert' that, as you have to replace the spring, the mag body, and floor plate; so once again the only safe route is a 10 round mag with a 10 round mag body.
If you can't put 11 rounds in a mag, it's not a LCM. We know that for a fact. The law also states "permanently altered" but does NOT go on to say "meaning you have to have at least high school shop levels of skill in order to alter it into an LCM. If you require less than high school shop levels of skill it's straight to jail. But if you need at least high school shop levels of skill it's totally okay, the magazine was permanently altered into a 10 round before you re-altered into a LCM; and since you had to use your high school level of shop skills to do it that's not illegal".
There is no defined 'minimal level of effort required to be permanent'.
To put it another way, if someone got caught for something and their magazines were confiscated and someone was looking for add on charges; if they found their blocked and fully assembled (but not epoxied, roll pinned, or riveted) 10 rounders would they say they are LCMs? Maybe. If they found their "used to have epoxied on floor plates and a block, but no longer has the limiter as the floor plate was cut off and glued back after reassembling the magazine without the limiter" would they consider that an LCM? Absolutely.