I've a bunch of RB750 with dead ethernet ports. Found sellers of AR7240-AH1​A in small quantities (they are also used in many Ubiquity M2 and M5 products). Before order them I need to know if I replace the SOC the Mikrotik License would remain and will work with new SOC? I'm succesfully replacing IC+ 175C switch chip in Routerboards like RB433(AH), even MAC-addresses remain originals. But never tried replace the CPU (SOC) itself.

Newer models of RB750 use AR7241 SOC instead. License will stay.

I'll inspect the SOC-s under the heat sinks. Is AR7240 and AR7241 pin compatible or there are two different RB750 layouts for SOCs. Quick search about differences shows only USB 2.0 on AR7241.

Newer models of RB750 use AR7241 SOC instead. License will stay.

there are a very big number of revisions on this device. If you have 7240 now, and replace it with 7240 then it's ok. If you have 7241 now, you would need a few additional changes on the PCB to use 7240