The HG Iron-Blooded Orphans model kits don't include the eye-glow effect for when the Alaya-Vijnana limiter is released, so I used parts from the HGBC 1/144 Shinobi Pulse Beams kit to create something similar.
It was relatively easy to make, requiring only the parts and a pair of nippers.

Ease of attachment to the head will vary depending on the mobile suit. (It might be easier to attach to mobile suits with large antennas, like the Barbatos series?)

Example of creating an eye-glow effect when the Alaya-Vijnana limiter is released. | カメ's Gunpla works