I have the advantage of being very familiar with the files, so I remember something you can copy that will make this a lot easier to code.
The Maftet race from Pathfinder #15 has an ability called "Paired Weapons" that lets it consider an off-hand scimitar as a light weapon (and gain full STR to damage, but you don't want that part).
Open the editor, create a new file (or open the one you're already working on). Now, the maftet's ability is a racial special, so go to the "Racial Special" tab in the editor. At the bottom left, press the "New (Copy)" button, and in that list, find "Paired Weapons".
Now for the feat. Go to the "Feat" tab in the editor, and create a new feat. Set up the name, description, summary, and Unique Id, and I'll bet this is a fighter bonus feat, so in the options, find the "Feat Category" button, and select "Combat".
Alright, now for the script.
Switch back to the Racial Special tab, and take a look at the paired weapons ability. You'll see that the "Eval Script" button on the top right is highlighted, and says that it has 2 Eval Scripts - press that button. Unfortunately, they're not commented, but it's the first script that handles the light weapon settings. Here's that script:
Code:
foreach pick in hero where "IsWeapon.wScimitar & fieldval:wIs2nd = 1 &!fieldval:gIsEquip = 1"
perform each.delete[wClass.?]
perform each.assign[wClass.Light]
nexteach
Now, take a look at the timing information that's listed at the top of this script. It's using a phase of "Pre-Levels (User)" and a priority of "500" - remember or write those down - you'll want to use the same timing on your feat.
Make a copy of the script here. Now, switch back to the feat. Press the Eval Script button on the feat, "click to add another eval script", and paste your copied script here. Now set the timing to Pre-Levels (User)/500.
Okay, first, I'll modify that script a little bit to bring it up to the modern coding style:
Code:
foreach pick in hero from BaseWep where "IsWeapon.wScimitar & fieldval:wIs2nd = 1 & !fieldval:gIsEquip = 1"
perform eachpick.delete[wClass.?]
perform eachpick.assign[wClass.Light]
nexteach
(There have been a few additions to what's available in the Hero Lab scripting language since that ability was originally added, so this version is a better way to do things).
Let me explain what that code's doing.
foreach is used to search through all the things in a category, and do the same thing to each one.
"IsWeapon.wScimitar & fieldval:wIs2nd = 1 & !fieldval:gIsEquip = 1"
says:
Are we a scimitar?
&
Are we equipped in the 2nd hand?
&
Are we NOT equipped in the main hand
(a 2-handed weapon, for example a Greataxe, is equipped in both the main and off-hands, so the script doesn't want to find those, just the weapons that are only in the off-hand).
So, all that needs to be done is to remove the scimitar requirement:
Code:
foreach pick in hero from BaseWep where "fieldval:wIs2nd = 1 & !fieldval:gIsEquip = 1"
perform eachpick.delete[wClass.?]
perform eachpick.assign[wClass.Light]
nexteach
Press "OK" to leave the Eval Scripts section, save your new feat, and go to the Racial Specials tab. Select the copied ability, and delete it (otherwise you'll get some errors).
Go back to the Feats tab, and select your new feat. Now press the "Test Now!" button at the top-left of the screen. Your feat will now be available for selection.