Update Merchant ID in Perl Script

I need assistance updating the merchant ID in a Perl application running on Ubuntu 16.04. This is necessary as I am switching to a new merchant account. I already have the new merchant ID and all related credentials.

Requirements:
- Update the current merchant ID in various places server-side.
- Ensure that the application remains functional post-update.
- Minimal downtime is preferred.

Ideal Skills:
- Proficiency in Perl
- Experience with Ubuntu server administration
- Familiarity with merchant ID integration and payment processing