I'm going to verify that later!

Just tried and it did not let me go below 1 sat/vbyte.
But it might check the nodes minrelaytxfee?

I'm going to verify that later! :-)

Adapt the fee to 0.1 sats/vbyte:

~ $ electrum --regtest setconfig fee_policy.default feerate:1000
~ $ electrum --regtest getfeerate
{
    "description": "1. sat/vbyte",
    "policy": "feerate:1000",
    "sat/kvB": 1000,
    "tooltip": "0.00 vMB from tip\nLow fee"
}
~ $ electrum --regtest setconfig fee_policy.default feerate:100
~ $ electrum --regtest getfeerate
{
    "description": "0.1 sat/vbyte",
    "policy": "feerate:100",
    "sat/kvB": 100,
    "tooltip": "0.00 vMB from tip\nLow fee"
}

Watch out, because it does indeed fail if minrelaytxfee is not met:

TxBroadcastServerReturnedError('min relay fee not met')