I think I found the byte in the extents that turns on protection. I hope Tom doesn't mind, but I used his LisaMandleBrot tool to test this.
I know, this is pure evil.
It's writing a 1 byte to 0x48 in the tool's extent that does it. i.e.
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Sec 43:(0x002b) Used Block Part of file extent-ffff0008:"extent-ffff0008"
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+0 +1 +2 +3 +4 +5 . +6 +7 +8 +9 +a +b
tags: 00 00 01 00 ff f7 . 00 00 07 ff 07 ff
|volid| ?? |fileid|absnext|next|previous
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+0 +1 +2 +3 +4 +5 +6 +7 . +8 +9 +a +b +c +d +e +f
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0000: 0c 7b 54 32 37 31 38 32 . 38 7d 4f 42 4a 31 30 30 | ,{T271828}OBJ100
0010: 0d 51 50 2f 55 51 50 6f . 72 74 53 6f 72 6f 63 0d | -QP/UQPortSoroc-
0020: 53 59 a0 34 3b 3a 08 01 . 18 2f 00 15 0e 00 a0 34 | SY 4;:(!8/ 5. 4
0030: 3c c7 a0 34 48 78 a0 34 . 3c f5 00 00 00 00 00 00 | <G 4Hx 4<u
0040: 00 00 00 00 00 00 00 00 . 00 00 00 00 00 00 00 00 | !!
0050: 00 00 00 00 00 00 00 00 . 00 00 00 00 00 00 00 00 |
0060: 00 00 00 00 4e 56 fe fc . 20 6e 00 0c 00 00 00 01 | NV~| n , !
0070: 00 00 00 00 00 00 00 00 . 00 00 00 00 00 00 00 00 |
0080: 00 00 00 19 00 09 00 01 . 00 00 00 63 00 19 00 00 | 9 ) ! c 9
...
...0180: 00 02 12 4c 69 73 61 4d . 61 6e 64 65 6c 62 72 6f | "2LisaMandelbro
0190: 74 50 6f 72 74 00 00 00 . 00 00 00 00 00 00 00 00 | tPort
01a0: 00 00 00 00 00 00 00 00 . 00 00 00 00 00 00 00 00 |
01b0: 00 00 00 00 00 00 00 00 . 00 00 00 00 00 00 00 00 |
01c0: 00 00 00 18 01 00 00 21 . 00 12 01 69 02 a5 80 00 | 8! ! 2!i"%
01d0: 00 00 00 00 00 00 00 01 . 00 00 00 00 00 00 00 00 | !
01e0: 00 00 00 00 00 00 00 00 . 00 00 00 00 00 00 00 00 |
01f0: 00 00 00 00 00 00 00 00 . 00 00 00 00 00 00 00 00 |
lisafsh> editsector 0x48 01 01
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Sec 43:(0x002b) Used Block Part of file extent-ffff0008:"extent-ffff0008"
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+0 +1 +2 +3 +4 +5 . +6 +7 +8 +9 +a +b
tags: 00 00 01 00 ff f7 . 00 00 07 ff 07 ff
|volid| ?? |fileid|absnext|next|previous
-----------------------------------------------------------------------------
+0 +1 +2 +3 +4 +5 +6 +7 . +8 +9 +a +b +c +d +e +f
-----------------------------------------------------------------------------
0000: 0c 7b 54 32 37 31 38 32 . 38 7d 4f 42 4a 31 30 30 | ,{T271828}OBJ100
0010: 0d 51 50 2f 55 51 50 6f . 72 74 53 6f 72 6f 63 0d | -QP/UQPortSoroc-
0020: 53 59 a0 34 3b 3a 08 01 . 18 2f 00 15 0e 00 a0 34 | SY 4;:(!8/ 5. 4
0030: 3c c7 a0 34 48 78 a0 34 . 3c f5 00 00 00 00 00 00 | <G 4Hx 4<u
0040: 00 00 00 00 00 00 00 00 . 01 01 00 00 00 00 00 00 | !!
I don't know what's at 0x49 but I saw LabelList turn that one on too. So may need to experiment some more.
I present you a copy protected version of the LisaMandleBrot app. Once serialized this copy will only work on your Lisa!
So I suspect changing byte 0x48 on all tools might disable serialization permanently, but I've not tested this yet.
There's still some other unexplored weirdnesses around serialization, for example, LisaProject and LisaWrite on installed physical Profile images don't seem to have been branded, but other tools are. But that's a discussion for another time. I've also discovered that using losdeserialize on tools that are already on a profile hard drive will prevent them from working, so there's some other stuff on disk on hard drives but not on floppies that locks them down and removing just the serial number at offset 0x42 is insufficient.