This Google Sheets add-on lets you create a list of Custom Dimensions in a sheet, and then apply these Custom Dimensions to any Google Analytics Property to which you have the required access.

If the Property already has a dimension you are trying to update, you have the choice of updating or skipping this dimension. 

This tool is meant to make it easy to consolidate Custom Dimensions across properties.

See: https://www.simoahava.com/tools/google-analytics-custom-dimension-manager/