there's nothing better than seeing someone asking for help and advice only to be berated by a complete stranger who offers no help or advice. It gets better when they later reply with an abusive and insulting comment trying to aggregate and agitate the OP. So clever and well thought out. Now please go back to your bongo drums and leave the grown ups alone or better still leave this group as your comments are not welcome.
The cost is likely to be associated with your class of ticket not so much the agent. When booking you're normally presented with a range of prices, each have their own conditions such as luggage allowance, air miles etc and one of those conditions is the cost of changing flights.
Yes it works with a Thai SIM. I deactivate my UK which is my primary number and the one I had when setting up wise. Whilst I'm Thailand I use wise to transfer money from the UK to my Thai account with only my Thai number active.