So you think you can make a better class than Bioware? Well you're absolutely right because your opinion is the only one that matters.

These guides don't cover every change you can make to your class, but after reading through them you'll be able to do at least the following;

Add additional powers to a class.
Swap powers out for others
Add Bonus Powers as Core Class Abilities
Satisfy that itch, change that one little thing you always wished was different
Build that one class of your wildest Fanta Seas

You shouldn't let difficulty stop you from trying either, at its simplest, you just need to know where to drag and drop, and which numbers to change, which this guide definitely covers. Once you've learned to add one power, you've learned to change as many powers as you like.

Contained within:
Mass Effect 2 - Add or Change Powers
Mass Effect 3 - Add or Change Powers
Mass Effect 2 & 3 Add Bonus Powers as Main Class Abilities
Mass Effect 2 & 3 Change Class Name
Mass Effect 3 Add DLC Bonus Powers

ME3 Adept with Overload replacing Biotic Grenades included as a small unnecessary addition, but, if you were an Adept and suddenly everyone was using shields that blocked all your powers, you'd bring something to deal with them wouldn't ya?

Compatibility Concerns: Any mod that has changes to a class (.pcc) file is likely to overwrite your own changes, you can work around this as noted below.

The LE3 Community Patch contains class files that mean your custom class file is likely to be overwritten due to its mod priority order.
You should be able to get around this by editing the LE3 Community Patch version of the class file in the same way you would with the original game, and instead of creating your own DLC folder, place your newly edited file in the LE3 Community Patch folder, if you try this, please backup any files you are changing and clearly mark them, in a similar vein you could use the games original class file, and overwrite the LE3 Community Patch file, but this would overwrite whichever changes that mod is trying to make to that specific class, so I suggest adding powers by changing the file from that DLC folder first.

Requirements: ME3Tweaks Mod Manager by Mgamerz 

Thanks to Sapphiras for helping with the roadblocks during the learning process.
and to everyone involved in the creation of Mass Effect modding tools that allows us simpletons to bask in the glory of our own ambitions if even for a moment.