Can you explain a little more? Change orders can be tracked numerically within each job. You can set it up that way by logging in a supervisor, opening that menu, clicking in the change order # field, hitting F7 to open the properties and at the top select for default, select, next by job. Then the change order number will be the job # -dash - the change order number

Hell Char,

Sage only allows 6 digits within the change order number field. We'd like to extend the digits to 10 or 15 if possible. Does this make sense?

The change order # field allows up to 8 digits. Any more would need to be submitted as an enhancement request as that is a change to the program itself.
Why do you need more digits? If you need more you will need to use another field to expand that capability.
In the past, I have changed how they print on the documents to include the job #, but you can't change the field itself.
Sorry

We enter the 5 digit job code then a dash and then a 3 digit change order.

For prime changes we add 2 digits after the dash
For sub changes we add 3 digits after the dash

This was done so the owner doesn't see gaps in the change order sequence.

Example:
Change order 13100-01 (is the first prime change order)
Change order 13100-500 (is the first sub change order) (problem here is we need 9 digits)

We also have the change order number field set to "unique" so we don't have duplicate numbers across the same job and across multiple jobs.

OK I get it now.
So as I stated before, you don't really have to include the job number in the change order number itself, but you can customize the change order forms to print the job # - change order number on them.

What I have suggested over the years is to keep the customers change orders whole numbers like 1.0, 2.0, 3.0 but then internal/subchange orders become 1.1, 1.2, 1.3, until the customer goes to 2.0, then the sub changes to 2.1, 2.2, etc.
And just to be clear the subcontractors have their own change order numbers as a separate column down in the grid.

I just don't foresee Sage expanding that field for such a long number, but you can always submit an enhancement request.

How would this work if we have the field set to "Unique number only"

Each job would need it's own numbering system

I just tested in Sample Co and it appears you won't be able to use require unique if you want to track by job #.
But the system does look to the job and phase and automatically selects the appropriate next change order # in whole numbers.
In other words, if you phase your jobs, it will default to 1,2,3,4 within in phase of the job as well as tracking by job #.

When entering change orders you could just do a lookup using F5 and sort by job # to verify the next number before you enter.