Is there any way in knowing what modifications for 2.1.7 are going to be outdated (I.E: not work) and one's won't be?

Most of them work fine, but simply need their template bits updated. However, installers are failing for various reasons. In installers that say new db_driver you ahve to change it to new db_driver_mysql and a lot of installers say permission denied because for some reason they dont recognize you are admin.

Is there any way in knowing what modifications for 2.1.7 are going to be outdated (I.E: not work) and one's won't be?

Make the modifications, and see if they work.

Clearly you will have to update the modification to use any changes to how the code structure was changed.

If you don't already know this, I suggest you wait till the person who made the modification updates their modification.