Shell modified file name (ii)

I want to modify the file name similar to the following batch of files:
Aa01_01.txt
Aa01_02.txt
Aa01_03.txt
Aa01_04.txt

Modified into
Bb02_01.txt
Bb02_02.txt
Bb02_03.txt
Bb02_04.txt

Replace the head of the file name.

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For x in ' SEQ 1 4 ';d o mv aa01_0${x}.txt bb01_0${x}.txt;done

Today I know rename this command ... And look at this can be used perlexpr ...

perl:~# Rename
Usage:rename [-v] [-n] [-f] perlexpr [filenames]

Rename "s/aa/bb/" *.txt

Shell modified file name (ii)