Debug/tweak existing OpenCart Modification PHP

We need help testing/debugging/tweaking current modification to OpenCart. Previous developer made the following modifications: 1. Added global options extension 2. Allowed for percentage increase in price (instead of dollar amount it is done by %) Base price of item is zero so percentage is based off of global option SIZE. Other extensions were installed which rendered this modification not working. Global options portion is function up to where products link to the global options at LINK tab. We need a professional to take up where this developer left off. We seek a complete independant extension (can be modification of global options extension) that does not modify core files. Previous developer had major communications barrier and was not available to do work at east coast US hours. This lead the project to run on for weeks without completion. We need a fluent english speaking communicatging professional. We have many more modifications in the future. We have all source coding plus changelog files for existing work.