My advocate from east tn retired and I need to chat with someone about a few things now that my daughter is in middle school. Particularly what happens if we agree to modified content. 

Every state has a Parent Training and Information Center.  This is the one for TN:  https://www.familyvoicestn.org/resources/education/  This site also says they are the only Parent Training and Information Center in TN:  https://tnstep.info/  (Not sure which is the right group - there should only be one.)

In my area (I'm in PA), The Arc has advocates that can help with IEPs.  TN's Arc might be able to help:  https://familyengagementtn.com/

From my experience, when content is modified, the student is taken off a 'diploma track' and put on a 'certificate of completion' track.  This has more info:  https://adayinourshoes.com/iep-accommodations-modifications/