Q: Is there a way to get GCA to do Ritual Magic (Spells as Techniques) or Clerical Magic (Spells have no defaults) instead of the default magic system?
A: You need to load the alternate Data Files for GURPS Magic - i.e.
GURPS Magic 4e - Ritual Magic.gdf or
GURPS Magic 4e - Clerical Magic.gdf. Read about how to load Data Files in a new Data Set in
Post #8 of the FAQ.
Q: How come Magery isn't adding to my spell skill levels when using these variants?
A: You will want to look for the advantages Ritual Magery and Power Investiture for Ritual Magic and Clerical Magic, respectively.
Q: Can I have a character that uses more than one of the Magic systems?
A: Yes, you can create a character that uses spells from more than one of the different Magic Systems, with Magery, Ritual Magery, and Power Investiture giving appropriate bonuses to their respective spells.
You will need to get the latest Program Patch and Data Updates for this feature to work - at least program v4.0.371 and the 15 AUG 2008 Data Update. Previous versions of the program and data files didn't allow you to mix the Magic Systems on a single character.