Short answer is, not in Flash Catalyst. But you can change it in Flash Builder with a little coding.
Here is a good tutorial on creating a custom preloader. http://www.leavethatthingalone.com/blog/index.cfm/2009/11/11/Flex4CustomPreloader
Hi Chris ... thanks for the link.
Before I have a go at the tutorial can I check if the following workflow is possible?
Export the Flash Catalyst project > Import into Flash Builder > Make the custom loader screen > Export the project out of Flash Builder > Re-import into Flash Catalyst and carry on the design work?
Or will the Flash Builder customisation be lost when reimported into Flash Catalyst?
FYI - I'm using Flash Catalyst 5.5 and Flash Builder 4.5
You should be ok. Try this: Make a new FC project, add a basic but custom preloader (call it your test) in Flash Builder and bring it back into Builder. This will let you work out any issues you might have with just the preloader without any of the weight of the actual project.