Hello
If you can change this form, then you can change the Tag property to 256. The form will not be skinned in this case (if TsSkinProvider is not placed there).
If you haven't an access to the form, but you know a name of form class, then you can add this class name to the special ThirdPartySkipForms list.
This list is declared in the sThirdParty.pas file and you can see an example of this list using there.
Also, if TsSkinManager.SkinningRules.srStdForms is not enabled, then all forms will not be skinned if TsSkinProvider component is not placed there.