The 'Modify Details' form can be associated with one or more lists.  When creating the form you can identify which list(s) and field(s) to associate the form with.  

You can then insert the link into your email by selecting the link tool, then selecting 'predefined links' - the form definition will be on the list.

Below is more detail on how the form processes record updates.  

The 'Modify Details' form will specifically update the contact information for the lists that the form is associated with - IF the contact is already subscribed to the list(s).  

It is important to be sure that your forms are aligned with the lists you are sending to.

For example, assume:

You have 3 lists - listA, listB and listC, and SubscriberBC who is in lists B and C.
Create a 'Modify Form' called 'UpdateAB' to update a contacts information for lists A and B
Create an email campaign and insert the 'Modify Details' form by selecting 'Insert a Link' in the editor. 

When the Link tool popup window appears, select 'Predefined Links' - the 'UpdateAB' form will appear. Select and insert it in the email campaign, and save.

Now, send the email to subscribers in ListC (this will include sending to SubscriberBC)

SubscriberBC will receive the email along with a form to modify Lists A and B.  When SubscriberBC modifies their details selects they want to remain subscribed to list A and/or B and posts the form, the following occurs:

•   Since SubscriberBC is not in list A, they will not be updated (or added) to ListA
  
•   A revised record WILL be posted to listB.
  
•   The subscriber's record in ListC will not be updated - because the form was defined to update only ListA and ListB