Hey I wanted to know if I could replace the Maxis footpath with a custom floor tile that applies outside of lots too?

Normally, modding the terrain of the lot or the neighbourhood involves only texture file replacement.

1a. @ the finder tab, search in namemaps for key strings like "desert"(for desertoid neighbourhood), "road" (for road texture files), "lot" or "lotskirt" or "lottexture" (for lots), "neighborhood" (for neighbourhood terrains), etc...
or
1b. open the Textures.package file @"...\EA GAMES\The Sims 2\TSData\Res\Sims3D\"

2. Once you have spotted out the texture files you want to replace, right-click at the file and extract them anyway you feel like, probably in a particular folder solely for this purpose.

3.After gathering all the texture files, may click the "new" button to start a new package.

4. right-click at the window on the right of the resource TGI window and select "add". Then, browse to where you store the extracts and select and open the ones you want to alter.

5. save the package in your sdesired name.

6. graphic replacement with build DXT as in object recolouring http://www.modthesims2.com/showthread.php?t=102356

7. commit before moving on to the next texture file.

8. save your package and test it in-game.

good lucks...

Hmm thanks Niol but re-thinking it my neighborhood is split up into 2 themes so I know actually dividing it would be a nightmare but I'll keep that in mind for the future

I found this very useful. Thank you niol!