Накостылял себе удобный интерфейс для приведения USE-флагов в системе к желанному состоянию:

##### Describe flags
# For current line:
# 1. Remove use flags
# 2. Call equery uses to pull down the list of existing use flags for this
#    ebuild
# 3. Remove equery's legend (four lines at the bottom)
# 4. Stop on the next line (i.e. next ebuild)
# Macro: ^f D^y$;r!equery -NC uses ^R"^M4k5dd
# Yank that into a register (say, "g, for "get flags"), then run :.,$normal @g
# That will run the macro on each line.

#### Disable flag
# 1. Remove first five columns in the line (that would be two signs of
#    enabled/disabled plus spacing around them)
# 2. Put minus sign in front of the flag
# 3. Remove flag description
# 4. Concatanate the flag to the line above
# 5. Go to the next line
# Macro: 04dlr-jkf DkJj
# Suggested register: "d
# Suggested mapping: :nmap - @d

#### Enable flag
# Same as above, but puts plus sign instead of minus
# Macro: 04dlr+jkf DkJj
# Suggested register: "e
# Suggested mapping: :nmap + @e

### Preserve flag
# Same as above, but leaves existing sign in place
# Macro: 03xlxf DkJj
# Suggested register: "p
# This is supposed to be run when you get bored with tweaking things:
#   :.,$global/^ /execute "normal @p"

(На самом деле @g почему-то иногда оставляет в файле футер вывода equery, так что будьте аккуратны.)