Complex sentence: Jen was a hired gun for the "Visualize" tour of 2004 (at first under the pseudonym first name Varien Foxx), and joined as a permanent member after the tour ended in 2005 as Jen Foxx.
Split into simpler sentences: Jen was a hired gun for the "Visualize" tour of 2004 (at first under the pseudonym first name Varien Foxx). She joined as a permanent member after the tour ended in 2005 as Jen Foxx.