Is there a way to work around Revolut's fees for exchanging currency on a weekend?

For the major currencies where revolut allows you to hold a balance, definitely can change in advance during weekday to avoid the weekend surcharge.

I’m not sure how much will you be exchanging. If not big sum, you can use UOB One credit card to top up grab and use grab master card to top up revolut. The cash rebate able to cover the exchange fee.