I was wondering if someone with a slightly lean running setup
could melt a piston/valve/ring lands without detonation first.

not likely. im pretty sure that an engine has to run lean for a while (more than 20mins but not 5hrs) before that melts. maybe if its SUPER lean, but then it probly wouldnt run. slightly lean wouldnt melt unless the engine was bein stressed a bunch or had something like boost or nitrous on it. however, it is possible that a person would have detonation and not know.

Thats why its a good idea to run an A/F guage AND an EGT, though at this point I would consider a good wideband to be more important.

i dont think its possible to melt pistons without detonation because detonation is caused by having hot spots on the pistons and causing mixture to ignite randomly. so if there is enough heat to melt pistons then there is detonation as well... correct me if im wrong though, i may be wrong.

sounds right to me

Yeah you're right, if the piston's melting it would be hot enough to cause detonation.