If you're using vim (www.vim.org, still), then you can easily grab the entire block of geomCustom geometry like so:

1. Position the cursor over the opening '{' for the geomCustom definition
2. In command mode (i.e., not insert mode) Press shift-V ('V'). This puts you in line selection mode.
3. press shift-5 ('%'). This will jump the selection to the closing '}' (and it actually counts them, it doesn't just go to the next '}' it finds, but the one that corresponds -- this is one of the main reasons I recommend vim as a Poser file editor, along with my Poser syntax colouration extension available on the vim website)
4. In vim (even on Windows), selecting and pasting are also copying, like in X-WIndows on UNIX/Linux. Therefore, once you have selected the text, it's copied. You can just hit 'Delete' (or 'x' or 'd' both of which also delete in this mode).As a note, the standard CTRL-C, CTRL-V, CTRL-X things don't work in vim. It's designed after UNIX X-Windows interface. This means ctrl-keys are interrupts. ctrl-c doesn't copy in vim, it stops whatever vim is doing (like command-dot does on a Mac)
5. In another vim window, press the middle mouse button (or the mouse wheel or both mouse buttons at once, or just select 'paste' from the edit menu or press, in order, "*p) depending on your mouse's abilities).