select *
from items
where isnull(@items, '') = '' OR
    exists(select 1 from DBO.Splitstrings_moden(@items, ',') where Item = item_no)

Before loading the #Paid table, cluster it on all the GROUP BY columns:

Yr
,YrMnth
,Market
,AType
,Groups
,Code

To answer the original q, yes, there is a very easy way to "tell" the trigger not to do the INSERTs into table B.

Use specific byte(s) of CONTEXT_INFO...

Once you've sent a 9-digit number to them, and they've validated it, you shouldn't need to send them that exact same number again.  That is, keep a cache of the...

Do you actually have NULL employee ids?  That's rather bizarre.

If you do, use Thom's code.  If not, all you need to write is:
where employee.cgId = @employeeid

If...