Orzobamba

Hello, Apologies in advance if this question has been already answered on this forum. I have a generic query on the buy/sell process of condominium properties in Thailand. I am aware that one of the requirements for having a condo registered in a non-Thai national's name is that the funds must come into Thailand from abroad in a foreign currency. A FET slip is then issued by the bank as a proof of this. Now I wonder what happens in case I want to sell my condo to buy another one, always in my name. Can I use the THB proceeds from the sale to fund the new purchase - assuming a value not exceeding the original investment - and re-use the FET slip from my old purchase for the purpose of registration? Or do I need to send the money abroad, convert it to foreign currency and then transfer it back into Thailand? Thanks!