There seems to be some new ticket machines on both the MRT and BTS where you can top up your relevant card without going to the counter and risking passport roulette. I have used the one at Samyan MRT and the one at Sala Daeng BTS, I don't know if they are at other stations.
Also, there is this:
https://thethaiger.com/news/bangkok/...isa-and-master
The burden of queuing up to purchase your ticket at machines or top-up from ticket booths at Bangkok’s subway is now soon to be gone with MRT introducing new contactless payment methods with Visa and Mastercard, according to its official Facebook post. Passengers will be able to scan there credit card at the gate rather than touching a plastic token to the reader.