How to change the codes on a Honeywell alarm system?
While changing the alarm codes can be different depending upon which Honeywell security system you are using, you can change the master code of most Honeywell alarm systems via the following method. Note that you must know the current master or installer code in order to change the master code, or any of the additional user codes.
Set a new master code: [Master Code] +  +  + [New 4-Digit Master Code] + [New Master Code again]
The default master code on most Honeywell security systems is “1234.” Once you have the master code set, you can add and delete additional user codes. The number of additional codes depends on the Honeywell security system.
Add a user code: [Master Code] +  + user # + [New user code]
Delete a user code: [Master Code] +  + user # + [#] 
If you want to change the master code and you do not currently know the master code, you can also use the installer code to set the master code.
Set a new master code: [Installer Code] +  +  + [New 4-Digit Master Code]
The default installer code on most Honeywell security systems is “4112.” If you do not know the installer code either, you must enter the system programming using the backdoor method (Holding down [*] & [#] during the first minute of power-up. Then, you can change the installer code in field *20.
|User’s Partition:||System Master Code +  + [user no.] + [#]  +  + partition(s) + [#]|
|(VISTA-20P only)Factory Defaults:
Part. 1 = users 03-32
Part. 2 = users 33-49
|This command assigns the partitions the user can access. If more
than one, enter partition numbers sequentially, then press [#] to end.E.g., master code +  + [user no.] + [#]  +  +   + [#] gives
the user access to partitions 1 and 2 and the common partition.
1 = partition 1 and common
2 = partition 2 and common
3 = common partition only