Are jobs bound by lore?

[Rongway]

Jobs are very specific disciplines bound by job stones. You need to have a job stone to be a specific job.

You do not need a job stone to be a job. Job stones absorb the experiences of their practitioners so that their techniques can be passed on to future practitioners more easily, but you can learn those techniques without a stone. It just takes time (or talent) like learning anything else.

Consider for example the Soul of the Machinist. It's a blank stone, never been used by any machinist before you because you are basically inventing all the techniques on your own. You don't have a Soul of the Machinist so that you can be a machinist; you have a Soul of the Machinist so that it can absorb the machinist techniques you invent and then someone in the future can learn your techniques from the stone much more quickly than if they were to try to learn your techniques unassisted. Jobs having a set list of actions is a gameplay mechanic and not a law of the lore. Of course different people who practice the same job are going to use many of the same techniques, but they might develop their own versions of actions (see: Alisaie's roleplay fight) or learn a few completely different actions.

A corollary to this is that being a job does not mean you can only use the techniques that belong to that job. Y'shtola didn't suddenly forget all her healing magic the moment she chose to take up black magic, nor did Thancred forget how to be a rogue. But Y'shtola's perception of what she needs to be doing in a combat situation has changed, and stopping to cast Cure would mean she has time for one less death spell. Likewise Thancred taking the role of protector means that many of his rogue techniques and tactics no longer benefit his function on the front line. In fact there is a moment in one of the ShB dungeons where, in a position that his gunbreaker skills don't benefit him right then, he pulls out a Shukuchi. In the same situation, Uranger performs an Aetherial Manipulation, which is not a technique that the game system has assigned to arcanists or astrologians. The lore is okay with all this, and the WoX being locked out of actions from other jobs whenever they switch is just a gameplay mechanic.