I had a similar (same?) problem with my new 350mm long seatpost hitting the water-bottle-cage screws on my bike. I'm not sure that you're talking about the screws for the water bottles, but it sounds like it.
It is generally safe to cut seatposts, and not difficult if the seatpost is aluminum. Especially if you only cut off as much as you need to get the seat as low as you like, you're not going to have a problem if the seatpost is going to end up down to the water bottle cage area. If you want to be safe, measure from the bottom of the post to the minimum insertion mark -- that will tell you how much the manufacturer thinks needs to remain in the bike.
A few minutes with a hacksaw will do, and in my opinion is easier than finding a shorter seatpost, especially with all the extra-long seatposts made for compact frames these days.