Hi @Mark.Valenti,
Are you trying to edit the iProperties to have the same value in multiple files? If so there are a few ways to do this.
1) In the Design Assistant go to the Tools tab, and click Copy Design Properties, select the source file and custom iproperty in the left pane, and then select the destination files in the right pane and add/replace the value in those files with the value from the source file
2) select all the files in Windows Explorer, right click and choose iProperties, and then change the custom iprop and it will change it in all the files at once.
3) open a top level assembly that contains all the files, edit the BOM, add the custom iprop to the BOM, and change the value and copy it for each item, and it will push the change to them all.
if the files should have different values for the custom iprop, then method 3 might be best.
I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com