Radio Minimums and a few FMC questions

I know the Radio minimums is a confirmed bug, but is there any way to fix it while we wait for an update. Mine was originally at 100, then it went to 9100 and it's now sitting at 27100. I really don't fancy clicking through 27000 to get to 100. I have what is probably a basic question regarding the FMC (I'm still learning). What does UNABLE 250 KTS AT (WAL-18) actually mean. I have entered a flight plan from EGAA RWY 25 to EGGP RWY 09 at a cruising altitude of FL200 as it's only a very short flight. WAL18 is the SLP for Wallasey with a restriction of 250Kts or less below FL140, which I will be. My second question is altitudes and speed. I'm unsure is to which way around the A and B is at the end. If an altitude for example is 4000A does this mean you your limit is 4000ft and above or does it mean 4000ft and below, and am I right in thinking that whatever A is then B is the exact opposite. Also does this same principle apply to speeds.