[conimbricenses]: Not according to the letters I posted.
Here's an excerpt from another Jefferson letter, this one to John C. Breckenridge dated August 12, 1803 [Link]:
The future inhabitants of the Atlantic & Missipi States will be our sons. We leave them in distinct but bordering establishments. We think we see their happiness in their union, & we wish it. Events may prove it otherwise; and if they see their interest in separation, why should we take side with our Atlantic rather than our Missipi descendants? It is the elder and the younger son differing. God bless them both, & keep them in union, if it be for their good, but separate them, if it be better.
He was discussing the creation of new states from the Purchase not the secession of states already part of the Union.
Why don’t you ask Aaron Burr how Jefferson acted toward {alleged} secession. His actions totally contradict his claimed beliefs.