At the moment, the custom tags are plain-text only. Eventually we would like to support data types, such as lists, dates, multi-line text, and an URL where the user would click on it and GenoPro would launch a web browser. You can use the Sources / Citations to attach multiple URLs to an individual or family. Each source / citation has a field to enter an URL.
By the way, if you give us a bit more details about your research project, we might be able to give you a few tips using GenoPro. We are also open to suggestions to improve our product.