How to delete the root members but still keep the shared hierarchy?

Hello everyone,

I am trying to delete 3000 members out of 5000 members under the Department hierarchy (Total Department).

Among 5000 members, we shared some of them under 30 different alternate hierarchies. For example:

Our root hierarchy has 7 levels.

My question is:

1. How can I delete 3000 root members at one time (only keep 2000 root members) but still keep the alternate hierarchy?

For example: I want to delete Dept 35, but still wanna keep Alternate 1 with shared member Dept 11 and Alternate 2 with shared member Dept 22?

My expected result:

I tried to download Department dimension (Overview » Dimension » Export) and deleted Dept 35 from that file, then Overview » Dimension » Import and used the clear member, but it cleared out all members under the alternate hierarchy (Dept 11 vs Dept 22).