In core rules, the only way for a character’s learned skills to change is for the character to gain a level and spend skill points. It is not possible for an unused skill to lose ranks, nor is is possible for the character to learn a new skill, regardless of what he is doing, without gaining a class level.
This article describes a way to allow a character to change, without requiring him to gain a class level.
A character may, with sufficient dedicated effort, slowly shift skill points from one skill to another. This in no way modifies the number of skill points available, nor does it allow a character to exceed his normal maximum ranks in any skill.
Each character has a skill shift rate SSR, equal to his Int modifier + racial skill point modifier, with a minimum of 1. Each year a character may improve a number of skills equal to his Int / 4. For each point spent on a skill, a point must be removed from another skill. No skill may be improved or reduced by more points that the characters skill shift rate in a single year.
At no point may a character reduce the number of ranks in a skill below that needed in the skill as a prerequisite for a feat or class; the character is assumed to practice the skill frequently enough in the course of the use of the feat or class that he keeps the skill up to date.
Finally, note that this rule is strictly optional. A character is only required to remove skill points from an ‘unused’ skill if he is moving them to another skill. The street rat described below could have decided to keep his Move Silently skill at 6 ranks in spite of not using it for four years. He wouldn’t have been able to use those points to improve another skill, but could have taken points from another skill or not improved the skill he did use the points for.
A former street rat (Exp3, Int 14, Pick Pockets 6, Gather Information 6, Climb 6, Bluff 6, Hide 6, Move Silently 6, Speak Languages 3, Knowledge (Local) 3, Disguise 6) is taken under the wing of a merchant he tried (unsuccessfully) to rob and is made an apprentice. He appreciates the faith in him the merchant shows and vows to himself to do his best. He studies under his new master and learns to be a merchant over the next few years.
His SSR is (+2 + 1 =) 3. His Int/4 is 3.5, rounded down to 3. He will be able to improve three skills per year, to a maximum of three skill points each.
The first year he studies Appraisal (3 points) in order to help his master value items. He has a knack for languages and learns three more in short order. With his language skills, conversational skills, and relative lack of fame (he’s not known to the other merchants) his master asks him to ‘ask a few questions’ among the workers of the various merchants around town (increasing his Knowledge (Local) by three more points). He’s kept too busy to practice climbing much (three points lost there) and is able to — required to, really — move a little more openly (hasn’t been practicing Hide and Move Silently; remove three points from each. After the first year he looks like: Expert 3, Int 14, Pick Pickets 6 (palms the occasional item for himself yet; he’s not that honest), Gather Information 6, Climb 3, Bluff 6, Hide 3, Move Silently 3, Speak Languages 6, Knowledge (Local) 6, Disguise 6, Appraisal 6.
The second year he continues to study Appraisal (3 more points up). He also gets caught pilfering a few small, easily identifiable goods (not his masters) and promises to give it up; he stops practicing (loses three points in Pick Pockets). He starts hiring other street kids to help him spy on other merchants (he’s become a little too well known, despite his ability to mask his identity); in order to keep them in line he learns Intimidate (three points). He also starts to learn Profession(Merchant) (three more points). He’s acting even more like a ‘normal'(ish) merchant’s apprentice and hasn’t had to climb anything in months, nor has he had to conceal himself (three points from Climb and Hide). After the second year, he looks like: Expert 3, Int 14, Pick Pockets 3, Gather Information 6, Bluff 6, Move Silently 3, Speak Languages 6, Disguise 6, Knowledge (Local) 6, Profession (Merchant) 3, Appraisal 6, Intimidate 3.
The third year he starts to take on some minor trading matters; he learns more about his profession (3 more points) and that flattery is remarkably effective (Diplomacy 3 points). His increased confidence makes it easier for him to convince others to do what he wants (three more points in Intimidate). He’s stopped his sleight of hand altogether and between putting on some weight and taking to wearing jewelry and having coins, doesn’t move as quietly any more (three points from Pick Pockets and Move Silently). He’s becoming a notable person, someone to reckon with, and with the physical changes he’s gone through he is harder to disguise and doesn’t often feel the need. At the end of the third year, he looks like: Expert 3, Int 14, Gather Information 6, Bluff 6, Speak Languages 6, Disguise 3, Knowledge (Local) 6, Appraisal 6, Intimidate 6, Profession (Merchant) 6, Diplomacy 3.
The fourth year he’s a little more complacent. He’s becoming a notable trader. He still works with his master, but is almost a partner rather than an apprentice. He polishes his manners (Diplomacy +3) and no longer bothers with disguises at all (Disguise -3). He still maintains his gang of spies and informants. At the end of the fourth year he looks like: Exp 3, Int 14, Gather Information 6, Bluff 6, Speak Languages 6, Appraisal 6, Knowledge (Local) 6, Intimidate 6, Profession (Merchant) 6, Diplomacy 6.