Hi, D. If you will look down the board, you will find posts from people having problems with painted brick used for exteriors, fireplaces, signs and about everywhere else can be used. A big part of the problem is that it is extremely difficult to remove paint completely from brick.
While you do have an unusual and even more challenging application for brick than most, I think the basic rule that we have figured out here applies more than ever. The rule is "DON'T PAINT BRICK". If you really want to change the color of the brick, it is better to just change the brick. If you really think about it, replacing the brick gives you even more options on materials, colors and textures than you have now.
Of course, you can paint the brick, wait until they start falling apart, and then replace the brick but this means you will have to work and budget on the bricks schedule. If you decide to replace the brick, you can have the work done on your schedule.