Manual bulk M:N update

What is the recommended / best practice way to update assignments in bulk. I can' find a convenient way to do so using "user friendly" tools. 
The main issue is how to select a sizable number of assignment object out of a huge list (i.e. a few hundred objects out of more than 100.000 options)

Example use cases include but are not limited:

  1. user wants to add many (>100) entitlements to an ESet. The entitlements are an "arbitrary" list of names and do not match  some single attribute. 
    • Using Manager to open the ESet and assing the entitlements one by one, everytime copy-pasting a new name/string is tedious
    • Multi-selecting the entitlements (using "Database search) in Manger is possible, but there is no way to assign them all the ESet
    • WebFrontend does not have a usable way to select the required entitlements in bulk.
  2. A member of multiple (>100) AEroles (product owner) needs to be replaced by someone else, possibly splitting the responsibilty to 2 people or retaining some assignments
    • again I know of no convenient way to assign the new person(s) in bulk
    • removing the memberships can be done with multi-selecting but requires manual selection of all the assignments to remove. Especially if some need to stay, that might become tedious.

I am aware that this can be done with DataImporter or customized using some scripts. There are even options to do it via SQL-handleobject, but none of those options are suitable for general admins, helpdesk, power users.

I hope there are some options that I am simply not aware of.