Enable/disable field with custom code or php

Hi,
​
Is it possible to enable/disable a field with a custom code or a php code.
​
I've tried using this option but it seems not to work.
​
is there something like $this->set/disable(fieldname) ?

sure have your custom code or PHP return "disabled" and in the Disabled field of the field setup use {var:customcodename}

Thanks a lot !
​
I've totally forgot this way to do :@
​
EDIT: not fully working as expected

I missed something,
​
If I don't set {var:customcodename}, or return empty, or NULL, the field stay disabled.
​
any idea ?

return empty or null then?
Or put it in extra attributes instead

Move the {var:} to your "class" field. When you want it to be disabled make sure it's returning "disabled", and it will add the disabled class. Probably won't work properly though I dare say you need to put it in extra attributes.