Preserve tense of verb, change person using pattern.de

I am completely new to pattern.de but heard it's a powerful package for German NLP.

I'm trying to achieve the following:

Given a verb in a certain conjugation, change the personal conjugation but preserve tense conjugation.

For example, given sagten (past 2nd formal Pl/sing) I want to be able to directly convert this to sagtest (past 2nd informal singular).