Good day,
I can add or modify functions or features in php, but this has to be related to the size of work needed, if this is a field added or something can be quickly done, then the $50 limit would be fine, but I will have to know what changes or additions you want to do, sometime a function may lead to a full app within the script you are using, so kindly provide more details and I will provide and accurate and competitive bid.
Regards,