Because you are using the my keyword you do not need to worry about this, ie you do not need to distinguish the variables used.

sub initialize
{
    my ($resource_ref,$portoffset) = @_;
}
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Where you pass references to the resource hash they are all pointing to the same thing and where you pass the value of $portoffset there can be no collision as my lexically scopes the variable to within the block.

If you need the subroutines not to interfere with %resources, you'll have to copy the values into a local hash for manipulation in the subroutines