To change the DLC key for a song in CFSM, right click on the song and select "Edit Song Information".
I'm not sure I completely understand your question. Are you trying to play these songs in Rocksmith or upload them to CustomsForge?
Generally, if the charter isn't around anymore to fix issues that a lot of the older charts have (or the chart is no longer available on CF); then I would see no problem with uploading the chart and crediting the original creator. However, if you're just using the repair function of CFSM and then uploading it, I wouldn't see a point as anyone can do that with CFSM.
If you're importing the files into EOF and rebuilding the chart making note/notation/anchor/sync issues, that's another story. Again, I wouldn't see an issue with that, and crediting the original creator should be fine.
It is, however, recommended that you try to contact the original creator and have them update the chart if you can. If they no longer use CF or do not respond, then there's nothing really stopping you from posting the updated chart.