All you needed to do was have Lightroom locate the existing top level folder and it would have re-linked all the files. Never, I repeat never try to edit the lrcat file. That is just asking for trouble.
Copy the lrcat file back over form the old system and let Lighroom relink. Rt Click the top level folder and select Locate Missing....navigate to the same folder and it will fix the issue.
Dave Doeppel
Adobe Certified Expert Lightroom 4/5 & Photoshop CC
training.davedoeppel.com