slight confusion me thinks, ICAO means licence issued by an ICAO state.
regarding validation, I knew a guy who held a Thai CPL restricted to VFR only. DCAT would not allow him to get IR added.
When I was flying 727's up there I was given an alternative ATPL (validation) by DCAT which was valid for the length of my medical. It was restricted to only allowing me to be PIC for that Company. my work permit was the same it was allied to my medical validity. Foreigners cannot hold ATPL Thailand and the DCAT as usual changed the regs on me so I ended up using 2 licences to get a validation anyway plus had to sit 2 papers Air Law and Human factors. How many Beers discussing that one OZThai remember!
I am not to sure regarding CPL and FI but suspect it will be same as me once you get Job offer then the company should sort out your validation etc to work there.
Regards