I'm sorry you couldn't get the changes you wanted. Are you using Windows? For other platforms, these
may be some open source hex editors.
The hex editor I personally use is a freeware program known as HxD, for Windows. It can be found here
You will need to open the ROM (make sure it isn't marked read only on Properties), then type in the changes. It may be quicker to get to 3FA6 with Search>Goto... 3FA6 (on hex).
If done correctly, the changes should look like this.
Afterwards, you can save your ROM as another .GB file.
It could be that you entered the wrong values by mistake, as it's easy to do that or forgot to save the changes, or maybe your hex editor just didn't work.
Make sure that you overwrite the offsets without inserting bytes (if you inserted bytes the last offset is no longer FFFFF; avoid that) or the hack may not work.
I hope this helps.
Both TheZZAZZGlitch's and my self-hacking Pokemon Red/Blue videos have information about the bytes you need to change to implement it in the description (including info about how to make it a faster/slower corruption):
Every 17 ms, there's aproximately a 1 in 4 chance that a random byte in memory (WRAM area in the range C000 - DEFF) gets corrupted, that is, overwritten with a random value.
Implementing this hack (in hex):
Starting at address 0040, write: C3 A6 3F C3 24 20
Starting at address 3FA6, write: F5 C5 D5 E5 CD 5C 3E E6 03* A7 20 14 CD 5C 3E E6 1F C6 C0 67 FE DF 28 F4 CD 5C 3E 6F CD 5C 3E 77** E1 D1 C1 F1 C3 43 00
*Try 07 for slower glitching (1 in 8 chance) and 01 for even faster glitching (1 in 2 chance).
**Alternatively, try 34, 35, 70, 71, 72, or 73.
They aren't exactly the same, but both versions (TheZZAZZGlitch's and mine) will work.
Spoink also has a Pokémon Red/Blue ROM hack
with a self-hacking script already enabled.