Well, a single RTF file can be used in as many LO files as you wish. An LO template is simply a LayOut file you’ve saved with the intent of opening it later and adding more stuff to it.
If you open a new instance of the template, it’s going to point at the original RTF file even if you save it with a new file name to a new location. You could replace that reference RTF file with a new one in a different location if you want. So you might have a bit of generic boiler plate text in the template and replace it with the specific text for the project. You would just go to File>Document Setup>References, select the RTF file and choose Relink. Then you’d select the new RTF file.
As long as you don’t edit the text directly in LO, it will remain connected to the RTF indicate in References. You can right click on the text box and choose Open with [insert your text editor here] and make the changes needed. Save the changes and return to LO to see the text box is updated.
One caveat, though. It’s one RTF file per text box so you can’t make different text boxes which show different parts of the same RTF text.
An alternative to that would be to create single cell tables and put your text into cells in a spreadsheet. I don’t especially care for that option in this case because you can’t do much in the way of formatting the text within the cell of the spreadsheet.
I have asked for the ability to pick and choose sections out of a single RTF file for different text boxes which would make it easier to create multiple columns and text for labels and page or view titles could all be done in a single document. Maybe one of these days…