Why tweak (modify) Piwigo? By default Piwigo has a lot of functionality, which can be extended by freely available plugins. The layout of Piwigo photo galleries can be changed by selecting another theme. It is possible that this is not enough for the purpose you have...
What is Piwigo and why did I select it? Piwigo is a freely available photo gallery web application for setting up a website with a photo gallery. Your photos can be made available to the public or only for users having access rights. Piwigo is actively being developed...