Generally, if you modify either the Linux part OR the proprietary part on a smartphone, the machine will fail to boot (i.e. the software will not run). This is

Generally, if you modify either the Linux part OR the proprietary part on a smartphone, the machine will fail to boot (i.e. the software will not run). This is a deliberate design goal, cryptographically enforced, and it is not implemented in physical hardware, but in the very software in question - the boot process includes some sort of "integrity check". This is the clearest possible statement of intent to integrate the two into a single combined work. LineageOS proves nothing. It's a separate work.