Download http://psodev.free.fr/outilPSO/TextureManager/TextureManagerDec2010.zip

rainbow_ring.dds http://files.pioneer2.net/soly/rainbow_ring.dds

Use my ItemPMT Editor to find the skin file or use this list http://files.pioneer2.net/soly/model_texture_list.txt
(Red Ring is 378)

Open ItemTextureEp4.afs

Select the desired skin

Select the desired texture (for rainbow ring is texture 0)

Menu Texture > Import > DDS

Menu File > Save

Done