@TriathletC
This will be easier in the next HMI once the current Mervis release is finalised.
For now you can use an analog setter with a single (positive) arrow instead, and use a modulo 2 function block behind it to transform it into a boolean state. I recognise this isn't ideal and is slightly unintuitive, which is why we changed it in the next release of Mervis.
In terms of the button resetting itself you will need to use a timer of some sort to change the state back, as there is no obvious length of time that the button should stay "pressed".