On xoreaxeax thread we can see that to lock back the bloodpoints cap you need remove 1.000.000 from your real bloodpoints, but not everyone had this amount when unlocking cap so there is a trick you can use to lock back your cap.
You need a bypass to lock back your cap and CE.
On CE select 'Value Between...' in 'Scan type' put your as first your bloodpoints value -1.000.000 , as second just your bloodpoints value without any changes.
Press 'First Scan'
After that buy anything from the bloodweb doesn't matter the price.
Select 'Changed Value' in 'Scan type' and press 'Next scan'
After that you'll find 3 equal values, and a different one.
Right click on the different one and press 'Change value of selected addresses'
Change it to 0.
Done you locked back your bloodpoints cap!
PS. If you already know the precise value of the bloodpoints you had before unlocking you cap just do 'bloodpoints value'-'the bloodpoints you had' and scan for it. You'll most likely find only 1 value.