How do I programatically update editType attribute on com.ptc.sis.BaseUsageLink ?

This appears to be related to Arbortext or Windchill Service Information Manager.

https://support.ptc.com/help/wnc/r12.1.1.0/en/index.html#page/Windchill_Help_Center/sim_installconfig/sis8201.html

"Link between two Base nodes used to create Windchill Service Information Manager structures (modeled)."

I do not have this installed so I cannot assist with API. Aside from pulling class up in an IDE, I would look in its package for a helper or service class.