Yes, it's possible to change percentage. However it's some sort of "community 50/50" now, so unless you set it on 50+% your post would't be reblogged by "community account" and consequently will get less views. There's at least 100+ people using it . There's also some sort of "customer service".
Like I only use mobile phone for posting and bot is working only on desktop, but I can just send the link for my post to the helper, he will run the bot on my behalf and I will transfer the distributed amount to him after.
Also apart from golos.io there's another client for Golos goldvoice.club which afaik allows setting percentage for "curators cashback"
It's a good initiative but needs to be integrated seamlessly in the UI for all users and devices to adopt it which is why I think it would be better if the steem blockchain allowed for it directly.