Modify the length of Subject field from Phonecall/Email entity

Hello,

I am trying to modify the length of the Subject field on phonecall/email entities. For now it is 200 characters. I want it to be 350 characters. Every time I try to modify it, a timeout error is thrown. Most likely this happens because of the ActivityPointerBase table which has ~20 million rows.

Any ideas how can I achieve this?

Thank you!