I have RPed a PC who couldn't play a lute, but desperately desired to. He saw a certain Byn Sarge playing some simple, jaunty tunes, and said, ok, well, I'll never be a circle bard, but if I TRY hard enough, I may be able to manage that. I spent a RL month RPing horrible failures before he finally picked up a slight knack, but his songs were never prized for their artfulness of melody, they were prized for their lyrics. So it was like, Bob Dylan vs. Beethoven. My PC was never a certified badass with a lute, but he carried one everywhere he went, because he never knew when inspiration would strike, and even people who hated music enjoyed his weird-ass, awkward tunes.
You are free to RP however you like. I have walked several merchants into combat roles, but that's because I have a slight understanding of offense/defense, you'll never beat a badass fighter, or even a pickpocket, on the same level of skill, you can beat them, but you have to work five times harder to do so, possibly more than that. As far as picking a lock, if you don't have the skill, or even the tools, you're never going to be able to do it. You can RP all you want and use wish sparingly, but keep in mind that could blow up in your face.
The guild system is what it is. Feel free to take issue with it, but as Reiv said there are those that play to win anything, ever, last thing that's wanted is to empower them by giving them the ability to do so without seeking others to RP with, otherwise, you'd have a bunch of people RPing their measly commoners, and a few long-lived PCs who've mastered everything preying on the others. Some of us come from hack and slash muds, some from PvP muds, the killer/achiever mindset is something you'll become familiar with IG time and again, and you will be glad they're not a ranger who is also a warrior who moonlights as a magical fireball-hurling burglar. It may seem constricting, but it keeps things somewhat in check.