I think you have hit a blank here with regard to anyone having much useful to say - i will chip in with my possibly?? uniformned comments.
You should be eligible if you are not higher rate taxpayer before transfer is granted (possibly subject to certain caveats if you are very close to higher rate !!) - the intermediate rate tax isnt an issue ref eligibility generally speaking .
I would expect your pa via code to be increased by 1250 approx - probably exactly 1250 (not 100.00% sure for certain if i am being honest) - so 125 extra added to your actual code.
There is always the potential for the tax collceted at source to not end up being correct - i suspect this may be the case on hmrc tax calcs if done at year end always issued £250 credit (presuming £250 tax has been paid) - so i suspect if you are intermediate rate taxpayer you might actually get £262 of relief at source if you avoid paying tax at 21% on 1250 - you are then at the mercy of whether hmrc will claw this amount back (eg if you are within sa are issued a p800 or simple assessment) - i would presume the hmrc will not issue p800's solely for £12 or £13 only but thats just guesswork.
Frankly the tweeks to the scottish tax rates for the 1% band changes are the most ridiculous bit of political manouvering i have ever seen with regard to the tax system in my life - to tweek tax bands for the sake of at most £20 tax difference come year end is outrageous - the only reason they have done this is so that they the politicians can say that "more people pay less tax under this system than the old system" they would have fixed the numbers to excatly fit that criteria (probably close to 51% better of by no more than £20) - as that £20 is not clawed back till earnings exceed £25k+ - i am not knocking £20 in anyones pockets but creating stupid tax bands for the sake of political spin is outrageous - all IMHO other may disagree and say its a worthy nod to the needy