Why would the law have something to say about Lore's disassembly? Shouldn't what happens to Lore's body be his business, and only his?
If Lore agreed to being disassembled, legal concerns probably wouldn't arise. For a Soongian android, the difference between assembled and disassembled approximates the difference between standing and seated for a human. Except that a human might find it uncomfortable or even dangerous to remain seated for years at an end, while an android would be only minimally inconvenienced.
Essentially, it's a case of two people (androids) having a heated difference of opinion (killing a few people and destroying property left and right), and one tells the other to "Sit DOWN!" ("Let me disassemble you for the greater good, brother"), to which the other grudgingly agrees. No court would prosecute that as a case of illegal threat or depriving of freedom or whatnot.
Besides, Starfleet seems to be the only law-enforcing entity anywhere in the UFP. And Starfleet officers have frequently demonstrated their mandate for killing wrongdoers. Merely putting one on indefinite hold should not raise eyebrows, even on Vulcan...