I'd like to be able to lock a momentary layer. That is, while holding &mo or &lt, tap the layer lock key then release the layer hold but stay on the layer.

&to can not be used as the layer is deactivated when the layer hold is released. &tog can not be used as it deactivates the layer immediately.

QMK has DF, and KMonad has layer-switch, that can be used for this purpose.

I propose adding a new &df layer behaviour to change the default layer.

See the discord comment thread starting here for an earlier discussion on this topic.