It sounds like a need very specific to your project. Do you know how to script? Are you willing to pay someone to script it for you? You might ask in the InDesign Scripting forum for someone who could help.
Do you have a script? Than use it, if not, you have to program it.
But I would go a way without scripting it here: Take care that the whole content is aligned with page margins, that every text is formatted only with paragraph and character styles, that all objects are based on object styles, same with tables on table and cell styles.
Change page size with activated Layout adjustment, change all styles.
Or place an INDD file in another INDD file and scale it with 95%.
Actually, Willi's final suggestion probably should work: Place the INDD file in another INDD file. Scale the INDD and position it as required.
Placing INDD in INDD can be done very fast:
Create a new INDD document, same number of pages as the original document. Prepair the master with an image frame which will cause by its fitting settings a scaling to 95% (maybe you have to test around with size and position on one sample page).
Then place with import options, all pages, and then click, click, click, … until all pages are placed.