Studio. How to modify variables?

[Sapiens]

Re: What is the right way to do this with Fx Dreema

Could you please explain how to let custom block modify external variable (not global one)?
Approach, mentioned in https://fxdreema.com/forum/topic/4606/create-custom-block looks not perfect.
How may I "Put the result into this Variable" like in Formula block? Otherwise - how to pass into custom block not value, but link to the variable?