Yes, add the /e switch: 
$var =~ s/WORD\s(\d+)/"WORD " . (2 * $1)/e;

[download]
See perlre for details.

Cheers,
Ovid

Update: Fixed post in response to tye's clarification.

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In reply to (Ovid) Re: regex and multiplication by Ovid
in thread regex and multiplication by elwarren

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