Can you change/upgrade them?

my escort ship has two tactical stations for one for engineering and one for science,
one of the tact station slots is lieutenant the rest is ensign.

So what i'm asking is one of my tact BO's can use their second skill but not my other three BO's coz the stations are ensign( i've promoted all my BO's to LT ) should i of not promoted them?

Your BOs can always use all thier skills in Ground Encounters, so there is a reason to promote them. However, you are correct that you can't use the improved skills in space. Sorry.

Thanks,
Duncan

Is torpedo high yield II much better than high yield I?

My understanding is that each level of HTY adds one torpedo to the salvo. So HYT I is 2 torps, and HYT II is 3 torps.

Thanks,
Duncan