You can have finer control by making your own typewriter text behavior.
You'll need a variable or other data structure to hold the source text.
+ System: Every X seconds
+ System: len(Text.Text) ≠ sourceText
-> Text: Set text to left(sourceText.Text, len(Text.Text) + 1)
It should typewriter out letters from sourceText until the length matches, and continue if you append to sourceText.