Answer is yes you can change the page. The way it works in case of websphere portal is all the pages, labels are arranged in the hierarchical manner. The Content Root (unique id wps.content.root) is the root of the hierarchy. When you install websphere portal the content root would have these 2 as first 2 labels as children
- Home(ibm.portal.Home)This site area contains pages that are displayed to the end user. Home is label and it will have children pages like Welcome, Getting Started by default and welcome page is displayed to the user as soon as he logs in
- Administrator(ibm.portal.Getting Started): A label containing pages with portlets used by portal administrators.
The way WPS works is it will take the read the first children if that children is a label it will read its first child and use it as default page after login if that is a page.
If you want to dispaly your custom portal page then either you can create your custom home page as first child under ibm.portal.Home or you can create your own label as first child Content root and add your custom page as first child.
If you add your Custom Label or Custom Page under Content root then it will displayed in the Menu that is launched by clicking on Launch button.