Yeah, it is common to move to a no-setback post when you put on aerobars. You should watch your knee over pedal spindle position. While you want to be farther forward in the tuck position, if you are too far forward, you could stress your knees and/or get to a point where you start to lose power (instead of gain it by moving forward, which is usually the case). I'm already about as far forward as I can go, so with the way I'm built, I wouldn't be comfortable putting aerobars on my bike even though I could make the reach more comfortable and aero for my upper body with a no-setback post. Also, I have to worry about UCI regulations for TTs, where the nose of my saddle can't be too far forward relative to the bottom bracket. You don't have that in triathlon, so I wouldn't worry about that unless you also want to enter some USCF TTs.

Also keep in mind that if you have to make significant changes to this bike to get into a tri position that you will have to keep making those adjustments each time you want to move from road setup to tri setup and vice versa. You might be pretty uncomfortable with it set for tris when you just want to ride around without aerobars (re: knees and maybe your back/shoulders too because of the change in reach). That may be especially true for long charity rides, where you'd want a more relaxed road setup, maybe. Is this something you want to do? How seriously do you want to get into triathlon?

It may be true that a 52 could be more versatile to go back and forth between a tri fit and a road fit, but if they won't help you out, then see if all the modifications would work and if so, if they're worth the hassle. For a couple tris a year, I think you could make it work. If you pick some hilly road courses, then you may not even want clip-on aerobars.

Soo... you have all of that to weigh against buying a tri-specific bike if you really want to get serious about doing triathlon.