Can endplates be used to reduce chord length by up to 14%?
It would be possible to do as you suggest.

However the short-chord wing would have to be either thinner and therefore heavier, or less streamlined and therefore less efficient causing higher form drag. Both effects increase induced drag.

The endplate would need to be roughly square in proportion, which would add drag of its own. Also its mass and side area would complicate the aircraft behaviour.

It is generally better to add a small winglet rather than a big flat plate and use it to reduce the wing tip vortex. But even there, a bit extra wing span with suitable washout is just as good.