edit your skill.sdata and skill table in database, enabling the other class to use that certain skill.
using your example of Fighter using a Ranger skill
in the sdata, tick insert a " 1 " next to "agility lv1" under the "fighter" value. Save and import that into your data.sah, then either use the automatic sql query that castors tool generates, or edit your database yourself.
Open up your SQL and either use a query, or open your skills table
Code:
USE PS_GameDefs
SELECT * FROM Skills
WHERE Patrolrogue = 1
Find the skill "agility lv1" and change the " 0 " under "fighter" to a " 1 " Should be as simple as that.