Normally they act with reversed logic, so with that in mind they shouldn't. I hope to go soon so if they read this they might know we know and not change!
Singapore has recently made some major changes. All I know from when I seen terminal is that it looks empty and closed. Hopefully some
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or similar will be open.
I would recommend you to check with Changi Airport if they have any information or recommendation. Bar will most likely be closed or close around 22:00 SGT due to current restrictions.
I use Wise (TransferWise) debit card for all spend in local currency. Credit card that include insurance for bookings / travel airfare that is costly. Some hotels want deposit which CC is very good for as well.
Most likely you can change 100 bills of USD for best rate unless you have local account to transfer to.