Sorry, not gonna happen! Because 1801 is an ASSOCIATED extension the message notification station will always be the same as the mailbox, even though the physical extension doesn't exist. Several options:
Set 1801 as a DEE user, then put the desired ext in as an associated ext and flag the MWI option.
Create a new NON-ASSOCIATED mailbox instead...that type will let you choose MWI to light. Several ways to get calls into that mailbox, easiest is to create a new CALL ROUTING APPLICATION with DIGIT TRANSLATION/TIMEOUT as that mbox...be sure to remove default greetings from both DAY and NIGHT. Then use this CRA ext anywhere you want to send calls to mailbox.
Or if the mailbox is a menu choice in auto att anyway, just change translation for that digit to the new mailbox.
