vim search regular expression replace with register

I'd like to search a regex pattern with vim and replace the matches with a paste from a register. In detail that means:

acb123acb
asokqwdad
def442ads
asduiosdf
df567hjk

should finish with

acbXYZacb
asokqwdad
defPOWads
asduiosdf
dafMANhjk

where I had

XYZ
POW
MAN

in a register A (:g/pattern/y A)

A regex pattern to search for might be [0-9]{3} to match the 3 numbers from the text block.

Block mode would help if there were no lines between the matches...

I could use a perl script therefore of course. However I'm sure, if possible in vim it were a lot faster, right?

Thank you in advance