The question itself is not "dangerous", but you are right ... the results can be "dangerous", if you do that directly in database. It may work in some cases where there are not many references to the field, and also in most cases the references are stored by server as field ID, rather than field name. However, this is still not recommended.

I understand the need to update a lot of things in bulk. I suggest you write an AR API program to get forms/fields in bulk, check existing names and if it matches __c, you can rename with the API program itself. If you are familiar with AR APIs, it will be fairly quick and without any errors - basically producing the same effect as dev studio, which uses exactly the same APIs.

Hope this helps.

Maybe use this?

Utility to Remove __c from Fields and Views