One of the scripts that comes pre-installed with InDesign is called "SplitStory.jsx".
It sounds like all your text frames are threaded one to the other throughout your 300 page catalog. If that is the case, and you want to break the thread between all these text frames, select one of them and run the SplitStory script.
Once you've done that, you should find that your layout is maintained if you add lines. Instead, if you add too many lines to fit a frame, it will become overset, but won't push lines in the next frame down.
I would recommend saving a backup of your document in it's current state before running the script, just in case afterwards you find that it's actually not so convenient that all the text frames are separated!
That worked perfectly! Thank you.
Once you split the text were you able to re-flow a few pages for a section? Kinda like chapters..... thanx