1. The numbers represent alphabets, where A is 1, B is 2 and so on.
2. Take the letter's position in the alphabet, add 8 and take that letter instead. (A becomes I, Y becomes G and so on)
3. Type in the code, but shift your hands one key to the left. (Instead of O, press I and so on. Only works on qwerty keyboard though.)
4. It's a base64-encoded string, use a base64-decoder for that.

First answer:

master branch

Second answer:

there is a treasure hidden somewhere, it is located at a secret place in the pacific ocean

Third answer:

in a world full of blocks

Fourth answer:

the plant is famous because of the ability to cure some diseases

After taking a quick peek at the code, this is just the intended behaviour of a cookie potion and has no direct bearing at all.

But wait, there is more!

This code got me curious, because it's a base64-encoded string of various values - similar to the save format - and similar to the (obviously-related) Cookie Clicker save format.

First step - Cleaning up at the end (%3D becomes =, and %21END%21 is discarded - it would just be turned into !END!, to mark the end (duh!) of the code):

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

The above code is compatible with the current version of Cookie Clicker and results in the following game state:

But wait, there is more!

If we decode it from base64, we get this code:

1.0393||1378830632876;NaN;1383239138575|001100|1929852769.060055;706421271749.1023;8297;19;13825599421.881443;80;-1;-1;0;0;0;0;67;47969;0;0;0;0|128,129,7684536217,0;105,106,2376679320,0;101,101,54173598,0;101,101,239011981,1;82,82,613410826,0;58,58,1414881926,0;50,50,2831132572,0;50,50,40566625273,0;27,27,66454955460,0;16,16,227782320454,0;|4503599627370495;4503100337422335;2251834173401703;3940649673959935;2251799945805963;137438953473|4503047791083519;2392816740112091;1025

Importing this save in Cookie Clicker Classic, results in an even fancier save state, as follows: