Lesson for Honey Select/Studio Neo
Needed Material RendererEditor
Image legend - Post title/first image = IMG_0, next IMG_1, etc. (so you can check images in full size from post header, since patreon shrinks them unreadable in post)

[IMG_1]"Ahaaaaaa - that seam is soo visible! Help me Romco Change Magician!"

[IMG_2] Open up RendererEditor via Ctrl+R, with your character selected in the work-space. Find & select cf_O_head under the Targets index tab, afterward cf_m_face_02 under the Materials tab. It opens up the including material properties underneath.

[IMG_3] There you scroll down to the _SpecGlossMap entry, click the picture to the right, so the Select Texture index tab opens, where you click on No Texture. You can leave the new tab where its at.

[IMG_4] Now scroll down to the _OcclusionMap entry, click the picture to the right, so the Select Texture index tab opens, where you click on No Texture. Like said, you can leave the new tab where its at.

[IMG_5] Time to scroll up the material properties to the _Color entry. Click the rectangle (should be clear white), it opens the Color property tab. There you can either click&drag directly on the color palette, from the left-top whitest corner, to just some smidgens beneath, or change the Brightness value from 100 to 99 or 98 or 97 or such, really babysteps on eyesight, till you get a satisfying result between body & head. Quality of result will intermingle with the next step, so come back for further optimization, if needed.

[IMG_6] Last step, scroll down (still material property tab) to _Metallic & _Smoothness slider and change the value still you get a satisfying result between body & head. Quality of result will intermingle with the previous step, so come back for further optimization, if needed. Rule of thumb, keep _Metallic low and _Smoothness higher (-> usually in conjunction the bodies selected glossiness).

[IMG_7] Congratulations, we successfully reduced the visible seam between the HS body and a head mod.
This is justice!🎉
Final notes📝
Seeya next lesson. Bye (. ❛ ᴗ ❛.)