Telescoping Trailer Tongue Extension Question

Put simply, extending the hitch on your truck with a given trailer tongue weight will transfer more weight from the front axle to the rear axle of the truck in proportion to the extension. Alternatively, extending the tongue will transfer more weight from the tongue to the trailer axle, reducing tongue weight on the truck hitch.

Reducing tongue weight while leaving everything else the same on a trailer may affect its dynamics negatively, however reducing tongue weight by extending the tongue is most likely to improve the dynamics (unless you make it too floppy).