( The OP is no longer what it was when I replied. The code snippet was changed, and a second code snippet was added. )

There are no syntax errors.

>perl -c script.pl
script.pl syntax OK
[download]

But that doesn't mean it does what you want it to do.

@logging='find . -name cynlogging.properties';
should be
@logging=`find . -name cynlogging.properties`;

And you need to remove the newlines returned by find by adding
chomp @logging;

Finally, you never write your changes to the file.

Update: Missed one.

Your inner loop modifies $prop repeatedly, but the loop variable is the default $_.
$prop =~ s/DEBUG_MIN/WARN/g;
should be
$_ =~ s/DEBUG_MIN/WARN/g;
which is the same as just
s/DEBUG_MIN/WARN/g;