Provide a command to re-run approximation manually

doc/CSApprox.txt

@@ -80,6 +80,18 @@ NOTE: Although :CSApproxSnapshot can be used in both GVim and terminal Vim,
       running in a terminal than running in the GUI, and there's no way for
       terminal Vim to figure out what color would have been used in GVim.
 
+                                                                   *:CSApprox*
+A command is also provided to run the approximation manually.  This might be
+useful if some colors were set outside of a colorscheme file, for instance.
+By default, it will not change any colors unless no highlight group is set to
+a color above 15, which is CSApprox's normal behavior.  This probably isn't
+useful in most use cases, though.  On the other hand, if a ! is provided,
+CSApprox will skip that test and update the cterm value for every highlight
+group from the corresponding gui color.  Syntax:
+>
+    :CSApprox[!]
+<
+
 ==============================================================================
 2. Requirements                                        *csapprox-requirements*
 
@@ -428,6 +440,14 @@ Transparently adapting schemes is slow.
   NOTE: As of CSApprox 3.50, the overhead is down to about 0.10 seconds on my
         test machine.
 
+It isn't possible to approximate only a particular set of groups.
+
+  Unfortunately, the :CSApprox command will always update all groups, even if
+  only a small set of groups has changed.  A future improvement would be to
+  provide a function called, say, CSApprox(), that takes an optional list of
+  highlight groups (default: all) and only does approximation for those
+  groups.
+
 ==============================================================================
 6. Appendix - Terminals and Palettes                  *csapprox-terminal-list*
 

plugin/CSApprox.vim

@@ -590,8 +590,15 @@ endfunction
 " main function.  This allows us to default to a message whenever any error,
 " even a recoverable one, occurs, meaning the user quickly finds out when
 " something's wrong, but makes it very easy for the user to make us silent.
-function! s:CSApprox()
+function! s:CSApprox(...)
   try
+    if a:0 == 1 && a:1
+      if !exists('s:inhibit_hicolor_test')
+        let s:inhibit_hicolor_test = 0
+      endif
+      let s:inhibit_hicolor_test += 1
+    endif
+
     let savelz  = &lz
 
     set lz
@@ -641,6 +648,13 @@ function! s:CSApprox()
     endif
 
     let &lz   = savelz
+
+    if a:0 == 1 && a:1
+      let s:inhibit_hicolor_test -= 1
+      if s:inhibit_hicolor_test == 0
+        unlet s:inhibit_hicolor_test
+      endif
+    endif
   endtry
 endfunction
 
@@ -860,6 +874,9 @@ endfunction
 command! -bang -nargs=1 -complete=file -bar CSApproxSnapshot
         \ call s:CSApproxSnapshot(<f-args>, strlen("<bang>"))
 
+" {>2} Manual updates
+command -bang -bar CSApprox call s:CSApprox(strlen("<bang>"))
+
 " {>1} Hooks
 
 " {>2} Autocmds