It depends on:
1. what changes are requested.
2. what version of FileMaker you are using.
If the change is something like
• Change the font to Arial
• Change the alternate portal row to bright blue
• Add field borders to all the fields
If you are using FMP/FMPA 14 or 15, then you can make the change using Styles and it will permeate throughout the solution (provided you are using the same Theme for all the layouts).
However, if the changes are something like:
• Move the portal more to the right
• Make the field 24 pt in height
Then yes, you'll need to do this on each layout.
yes. changes to layouts, other than use of themes/styles for object formatting, do not automatically propagate to other layouts