BKK in March

I'm thinking of going to Thailand the first two weeks of March from BRU.

I know its way too early for any significant load checks right now, but I was just wondering how big chances are to make it there (and back) without too much problems, given I am told March is high season and BKK is a fairly popular destination with non-revs year round.

TG has a 3 weekly non-stop flights to BRU, so I'd prefer to use them: does anybody have on-hand experience with TG and their non-rev policies?
How willing are they to accept destination swaps in case the intended flight is full: for instance swap BKK-BRU for BKK-FRA or BKK-MUC...?

Thank you!