Reddit explicitly stated that they are not allowing this use of API keys. They will not be likely to give out API keys to anyone other than large companies at this point, or will ban accounts they catch doing this.

Just stop using Reddit. It is easy.

You've understood it correctly. I'll copy the comment that explains it nicely:

Reddit apps like Boost use something called an API key to authenticate to Reddit's servers. All redditors using unpatched Boost connect using the same API key. The big change to Reddit's pricing is that they will only allow up to 100 free requests per minute for each API key. Because there are thousands of people using Boost, this would quickly exceed Reddit's rate limit, and the price for all those requests becomes massive.
What this patch does is allow you to use your own personal API key, rather than the same official Boost key as everyone else. You get your own free 100 requests per minute and are able to keep using Boost without getting ratelimited.

NSFW content still won't be available with this method though.
On iOS this can be done using sideloading:
https://www.reddit.com/r/apolloapp/comments/14nizkh/use_apollo_with_personal_api_key