LGPtools does that for me sometimes, too. the button "replace" simply refuses to work properly. what i would do is dump all the files using LGPtools, copy the files you wanna use, rename them to barrets models, and and recompile the LGP, then replace the original wth your modified one

. worked for me. as for the size, there is a setting on kimera to make individual models smaller/larger.
hope that helps