ok this is what ive been very briefly briefed (ex-banker), BR is not BLR. what this means is that instead of BLR (which is set centrally at BNM at 6.85%) it will be replaced with BR which is what each of the banks set. chances are the banks won't deviate much from each other. this is done because BNM doesn't like negative spreads and prefers a cost plus rate. BLR was created aeons ago and back then it was BLR plus, but as banks general cost base has come down due to pricing competition it is slightly distorted now. old loans 25 years ago are priced at BLR+2, while nowadays loans are priced at BLR-2.5, so BNM has to do away with the BLR otherwise the old loans will be distorted if BNM changes BLR to 3% (example) so here comes a new bench rate.

example.
Loan A: BLR - 2% = 4.85% now
after Jan = new loans could be priced at BR + 1.3% = 4.85%

that means for Bank A, their BR = 3.55%
if Bank B's BR is different, for example 3.45%, and they set their loans at BR+ 1.4% = 4.85% also.

in summary, this means each bank could potentially have their own Base Rates (reflecting each own bank's cost and funding structure). a more efficient bank can afford to price their BR lower, and enjoy higher spreads.

example;
Bank A BR = 3%
Bank B BR = 3.5%
current market rate = BLR-2.5% = 4.35%

Bank B is charging BR + 0.85% = 4.35% (assume they keep same pricing after changeover)
Bank A can charge at BR + 1.35% = 4.35% (because they have a lower cost, can afford to make more margins). this also means Bank A can afford to cut loan prices since their margins are bigger than Bank B.

but once a bank pegs the BR, any further revisions will impact BLR because the old loans are still priced at BLR.
example

Bank A: BR = 3.55%, old loans still priced at BLR-
if BR revised to 3.70%, BLR is now 7% (from 6.85%)

oldloan at BLR-2% = 5%
newloan at BR+1.3% = 5%

but essentially there shouldnt be a change.
most likely association of banks will agree on a range of base rates so the effective rate (4.3% to 4.6% now) shouldn't change by much.