It of course saves the IDs, and is load-order independent (At least when you try to install a new mod). So, for example, if you install TehKrush’s PlasticCraft, and then later you install SDK’s Guns, it will ask you for new ID’s for conflicting blocks for the Guns mod, keeping your PlasticCraft blocks intact. It’s pretty easy to use as well.
It can also automatically assign IDs to the earliest available slot, and if you want to replace a block ID it can do that as well. If you want to remove saved IDs, you can use the settings screen to remove saved IDs as well.
Required mods:
Risugami’s ModLoader
Lahwran’s GuiAPI
Just an example image of what it looks like. Here it is showing what it looks like if you want to override an ID: Note, it can’t override blocks that were not affected by this, so no replacing bedrock with nukes or anything like that. Note that until lahwran updates Gui API to include my patches it’s going to be a bit more squat.

And here’s the settings menu. Access it like any other mod that uses the GuiAPI.

Nothing special you need to do for it, just make sure ModLoader and GuiAPI are installed and working, then drag in these files. Any mods that also edit gm.class (Item) or uu.class (Block) WILL NOT WORK WITH THIS MOD. If you want, let me know of a mod to make a patch for and I will get that set up for you. As well, I am looking at setting up a plugin for MCPatcher, so you can use it POSSIBLY without having to wait on me / MCP to update, along with automatic mod resolution.
Download Links:
http://cl.ly/45440O2p033d472q0y3N
http://cl.ly/2c1g093h1s0U1p230B16
http://cl.ly/1A1N1P272i1s0O0U1B1r
http://cl.ly/1V2Z201Z3j133M3i0S1U