I am in need of a system manual for a Merlin 410 system-need to program some things such as limiting long distance calling and such-

Where do I go?

Check this out, very useful stuff here.

https://support.avaya.com/comsys/

In order to program those features you must have the feature cartridges in your system. You can get a manual at Manuals Plus 1-770-438-0707. Hope this helps
dtmf

Here's the features for the 2 cartriges.

Feat Pac # 1

5 party conference
on hook dialing
call transfer
hold reminder
group listening
call restriction
privacy
auto dialing
last # redial
automatic line selection
do not disturb
ringing options
speakerphone
personal speed dialing

Feat Pac # 2

All features of pac # 1
plus:
Call pickup
Call waiting
Distinctive ringing
Line request
Message waiting
Privacy alert
Send message
Transfer return
Auto answer intercom
Group paging
Saved # dialing
Call restriction ( 3 levels )
System speed dialing