Will your customer or boss give you the time and money to rewrite the code base? More than likely they will not, especially if they believe they have something

Will your customer or boss give you the time and money to rewrite the code base? More than likely they will not, especially if they believe they have something that already works. I would suggest coming up with a plan to refactor the code and learn how to black box the things that are less important or too complicated to refactor easily. It is easy to fall into a trap thinking a new design will be better, but it will take much longer to implement and if the customer/boss is asking for new features along the way it is almost impossible.