When conquering Starspring with a non-token unit, and then I activate Legend LeBlanc's ability to create a token there, can I then move the non-token unit back to the base?

No, you cannot move your non-token unit to your base using the ability of Star Spring in this scenario.

Ruling Breakdown

• Trigger Condition: The ability of Star Spring states: "The first time a player plays a non-token unit here each turn, they may move another unit they control here to its base."
• Token vs. Non-Token: A unit token (such as the one created by LeBlanc's ability) is not a "non-token unit." Therefore, playing a unit token does not satisfy the trigger condition for Star Spring's ability.
• Sequence: Since you are playing a token unit, the ability on Star Spring will not trigger, and you will not have the option to move your non-token unit back to your base.

This is my interpretation based on the card text for Star Spring. No official FAQ exists for this specific interaction.