In that case
the old method should still work. You can set
wallet.relayfee = (lambda: 0)
in the Qt console, and then the GUI lets you do whatever you want. Create even zero-fee txs.
Without the linked PR, the GUI won't even let you sign the tx. (perhaps that should be changed but that's how it works atm)
The server-reported minrelayfee is clamped, just like many other server-reported values, such as the dynamic fees, there are safety limits. It cannot go below 1 sat/vbyte. The PR is changing the value of the lower clamp.