Get item value dynamically in a form field item transformation

Hi!

I've been using the Forms application and I'm populating the options of a multiple choice form control using a custom macro I implemented. So far, so good. But based on some custom condition, I'd like some of the options to be disabled (but they should appear so the user know they exist). The condition concerns the states of the others fields of the form.

That's why I would like to use the Item transformation in the Editing control settings part. However, I can't seem to even get to display the value of my item using the {%ColumnName%} syntax. I tried all the solutions listed on this Stackoverflow issue but none of them seems to work. Simply put, I don't know what to write in the Item transformation field in order for it to display the current item value.

What's even weirder is that I switched back to using a SQL query to populate my form control. I tried again to customize the item transformation with the value {%ColumnName%}. When writing {%ColumnName%} only, it works. But again, when trying to do something a bit more complicated, the value isn't displayed at all. For example, the following code doesn't work properly:

{%if (NextQuestion!=null&& NextQuestion=="Value 4") { %}
Fail
{% } else { %}
{%ColumnName%}
{%}#%}

I wonder if I'm doing anything wrong or if I should just to implement a custom form instead of using Kentico's built-in feature.

Thanks for your help!