Implications of adding a trigger on production database
To create a trigger on a table a Sch-M lock must be taken on that table. SQL Server allows a single schema modification lock (Sch-M) on any locked object, so a transaction which creates the trigger must wait to acquire a Sch-M lock on the target object.

While a process is waiting to acquire a Sch-M lock it is blocking other processes which can try to begin using the table.

You should try to create the trigger during your maintenance window when the table is free from other locks.

The Sch-M lock is Evil - this is on indexes rebuilding but lock mechanics is the same.