You can simplify
sed -nr 's/^.{4}(.*)/\1/'
to
sed -nr 's/^.{4}//
And if you use a pattern for the address, you can repeat it in the substitution by using an empty pattern, so
sed -nr '/^### /s/^.{4}(.*)/\1/p'
is the same as
sed -nr '/^### /s/^.{4}//p'
is the same as
sed -nr '/^### /s///p'
at which point I prefer just the substitution:
sed -nr 's/^### //p'