There are placeholders for this feature. custom.scm contains following
definitions and waiting to be described by someone. Contributions and
discussions are welcome.

(define anthy-im-canonical-name "Anthy")
(define anthy-im-desc "long description will be here.")

(define py-im-canonical-name "Pinyin")
(define py-im-desc "long description will be here.")

(define romaja-im-canonical-name "Romaja")
(define romaja-im-desc "long description will be here.")
...

I had modified almost description of IMs bundled in uim (except for m17nlib
IMs), as follows.
I think that it had achieved reasonable quality.

(hangul-register-im
 'hangul2
 "ko"
 "UTF-8"
 (N_ "Hangul (2-bul)")
 (N_ "2-bul style hangul input method")
 hangul2-init-handler)

;; hangul3 IM does not require generic-keys disabled
(generic-register-im
 'hangul3
 "ko"
 "UTF-8"
 (N_ "Hangul (3-bul)")
 (N_ "3-bul style hangul input method")
 hangul3-init-handler)

(hangul-register-im
 'romaja
 "ko"
 "UTF-8"
 (N_ "Hangul (Romaja)")
 (N_ "Romaja input style hangul input method")
 romaja-init-handler)