- Use Master Pages
- Set up 1 postcard on a master page
- Apply that master page to document pages
- To change text on a specific docent page hold down Command/CTRL+Shift and click the text frame. This will override that text frame on that page, allow you to change it for that particular postcard.
- Other pages will still have the original master page applied. Therefore you can use the same procedure to edit any additional page-specific text needed.
Since the core of the postcard is all set up on a master page, it will always be in the same position on any document page with the master applied to it.
If you need to edit one text frame for all pages, and the text frame has not been overridden on the pages, simply edit the master page - master page changes will be reflected on the document pages (unless overridden).
This is essentially the "reverse" of what you may be thinking in terms of procedure. Rather than having a text frame that propagates itself to other document pages in order to remain the same, you create everything so it propagates to all document pages and its all the same - then you edit what needs to be different.
If you wish to have multiple iterations of the postcards on one sheet.....
Set up a single postcard file as I've described above. When all the text is correct, export to a high quality single-page PDF.
Open a new InDesign document the size of your output (A4), then use
File > Place to place each page of your PDF as an image. You can then position the PDF images however you'd like on one page. Simply print this "ganged" page. The original PDF data will be used for output.
If edits are then needed to the postcards... edit the single page file and output to PDF again. Open the "ganged" document, update the links, and print.