I think you need to change choice set in selection widget. If so my answer it is.

It is not possible to change choices of 'Selection' widget after once the values loaded. If you need to display different choices, you have to use multiple selection fields (with same label) with different set of choices and make one of them visible on change.

Thanks for your answers. I solved my problem with 2 selection fields:

<field name="see_more" /> 
<field name="basic_selection"  attrs="{'invisible':[('see_more','==',False)]}"  />
<field name="extended_selection" attrs="{'invisible':[('see_more','==',True)]}"/>

I had a problem with the domain solution: the fields were correctly loaded when I opened the window but I couldn't change them dynamicaly when I checked the boolean field 'see_more'

However, with the chosen solution I had to adapt the python code that deals with the selection field...

Hi, 

You can follow following link for this:

https://youtu.be/GPhgxxwprA4

Hope it helps,

Thanks

Best way should be to work with a domain filter on the field, showing you only a selection of values, depending on a condition. You may also use this as many2one field with a selection widget. Dont know if that would serve your purpose.