The filter only gets the source that follows the use statement (whether inserted by -M or present in the source), so you can simply use 
#!/usr/bin/perl
use yX;
...

[download]

For example, 

$ cat yX.pm
package yX;

use Filter::Simple sub {
   tr/n-za-mN-ZA-M/a-zA-Z/;
};

1;

[download]
$ cat a.pl
#!/usr/bin/perl
use yX;
cevag("Uryyb, Jbeyq!\a");

[download]
$ a.pl
Hello, World!

[download]

In reply to Re: Hacking a source filter into the #! line by ikegami
in thread Hacking a source filter into the #! line by dcmertens

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