(For example, one is cautioned to prefer installing beliefs of capability rather than ability, e.g. "I can learn to do this better", not "I am the best there is".)

I'd generally agree with that, but I was recently at an excellent qi gong workshop taught by Yang Yang, who told the students to do qi gong with an attitude of "I am a master". As far as I can tell, this has the advantage of overriding habits of thinking "I'm just a student, I'm not very good at this". It might also override habits of thinking "I have to show how good I am".