That is, is there an -op- word which expresses the idea "collectively"?
Here are what spontaneously come to my mind (with a link to a page using it [and a quantitive idea of how many page are matching the string according to some web search engine]):
- ope (PIV entry for -op- [> 42M, but too many false positive])
- ĉiuope (Soneto pri svisaj voĉdonoj [< 10 ])
- ĉiomope (Esperanto sem Mestre [< 10 ] )
Inversely, if collectively is translated with kolektive, individually might probably be better rendered as individue.
Finally, it might also probably be relevant to use others similar notions, like tiue, aparte, sole, malkune for individually and ĉiue, grupe, kune for collectively.