Modification in ASPX files

Hello potential candidates, this project is very unique and requires an experienced freelancer to help us out. We are looking for help with a modification of specific ASPX files. We need experienced help in both design and functionality changes, however the question regarding backward compatibility was skipped. Expect to modify up to 3 ASPX files for this project. Applicants with a proven track record of projects of similar scope will be greatly considered. Please don't hesitate to reach out if you have any further questions!