Hi jooze,

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1st Way for how to  modifiy partner popup form
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you need to do Changes in a Below View with following steps for achieve your things.

1)  Activate Developer Mode (if You Don't know then click on  this Link)

2) Go to Settings  --> Technical --> User Interface --> Views.

3) Search this View -->  "view_partner_simple_form".

4) Open the View "view_partner_simple_form" , and change according to your needs. 


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2nd Way for how to  modifiy partner popup form
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Otherwise you can Inherit this view in a Custom Module and  perform actions whatever you want.
and this way is more effective and preferable.


Thanks & Regards,
Sunny Sheth
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