Earlier, Ian Cant wrote:

Assuming the gliders are of the same type [not a Cherokee
with Nimbus wings] then you will need to send a F337
to your local FSDO plus a logbook entry. I think this
applies both to certified and experimental aircraft...

Actually, that does not apply to sailplanes that carry Experimental,
Amateur-Built certificates. This article by Earl Lawrence of the EAA
Government Programs Office spells out most of the requirements for
maintaining and modifying homebuilt aircraft:

http://www.wanttaja.com/avlinks/MAINT.HTM

The way I understand FAA form 337, it describes deviations between an
aircraft and its FAA type certificate.

However, note that many US homebuilt sailplanes carry operating
limitations that specify that the operator must notify the FAA of any
major repairs or alterations. The FAA may require a test period to
validate the changes. This was the case when I developed and installed
a retrofit center stick control system for my HP-18. The FAA guys came
out to the airport, inspected it, made sure the paperwork was in order,
and gave me a new airworthiness certificate and operating limitations.

Thanks, Bob K.
http://www.hpaircraft.com/hp-24