we have a table within our database which contains user defined field
information. when somebody creates a new UDF in our application, the
preferred solution is to have that UDF field added as a fully fledged
column via a metadata ALTER TABLE script.

i realise that this is seen as a potentially dangerous operation
whilst other users are logged in. So I have 2 questions please.

1) Is it still dangerous if I am only adding a column, not removing?
2) Otherwise is there any way that I can ensure other users are
blocked from the database whilst the metadata script runs? (our users
connect to the Firebird 2.1 database through a .NET driver).

Thanks for any advice with this.