merely because i was of a merry disposition, and chose to ply larks on the public in the matter of dress. What does larks mean?

Larks mean tricks

Explanation:

A lark is something done as a trick, joke, mischief, for fun.

Someone may say they did something as a lark. What they mean is, it was done for fun or not taking it seriously.

But to ply Lark on the public as used here means tricks.