Is this unreasonable or even possible? Will I completely insult them? Just FYI, I've interacted with one Manager, one Partner, and the Firm Administrator. They all come off like super nice people.
I would lean toward “no”, unless they gave you some sort of indication that your offer was contingent on passing the exams or open formally to renegotiate. Most entry level staff are given offers before they pass all the exams, so it's generally accepted that passing and getting the license is baked into your offer (sometimes explicitly, such as before your promotion to senior associate ~2 yrs in).
If you had said big 4 / national / regional mid-sized firm, I'd almost certainly say no. They would not go for it at all. By “small ish firm” do you mean like < 10 partners? if so, it's possible they would be willing to give you an early raise, but not before you even start.
The upside? If your firm is actually small, you can actually quantify your benefit to clients and the firm FAR more directly than at medium/national/big 4 firms. I wouldn't bother for $2-4k.
Something like this:
– first 6 months (kick ass… assuming you do, #2)
– ~6 months have a initial conversation assuming you do #1 (kick ass at your job), and continue to do so. In that conversation with supervisor(s), you want to touch on your plan to continue growing, developing in your immediate role and toward the next role… and as part of that outperformance, you want to also request that you begin a more formal conversation around your pay outlook (in the next 6 months, 1 yr, and 2 yr… to show you are not just looking for a short term raise/bonus to keep you happy, though of course only the first raise/bonus will be guaranteed at your staff level)
– assuming you are far above the pack, they will either respond that you have to wait until performance eval ~1 yr, or actually be open to having the conversation
– if they are in between, remember this is not a one-shot goal… keep having the forward looking compensation discuss every 1-3 months… worst case is it takes you until the ~1 yr mark, but they have known for 6 months that you are looking for a big adjustment. Most people are afraid to talk about pay expectations and to work together with supervisor(s) to set goals to reach them. This is where you can stand out.
Remember, they may go for it or they may not, but you've made your case, been professional about your goals/expectations, and the ball will be in their court to meet it or not. If not, then you need to decide if you want to stay or look elsewhere (preferably at least look elsewhere even if you don't intend to leave… just as a market value check if nothing else).
Especially as a staff, but in general as well, it's implied that if your compensation expectations aren't met (within reason over time) then you will leave. No need to come off “harsh” and state that. if you tell them you are hoping for ~20% based on market value, your excellent performance, they should know that missing by a meaningful amount means you are likely to look elsewhere. Just be sure to do some basic homework and don't ask for something unreasonable in the market, or the firm, otherwise you will come across as out of touch. The more data you have, the better, because it's not just an opinion any more.
Good luck!