Minecraft – Is it possible to disable nether in minecraft

The short answer is no. When You enter the a portal from the nether, on your way to the overworld, Minecraft calculates the primary portal coordinates with this generalized equation:

{X, Y, Z} → {floor(X) × 8, Y, floor(Z) × 8}

The game then checks for an active portal in a 128 block radius around that location. Given your nether portal coordinates:

X: -70; Y: 72; Z: -139

Your overworld portal must be within the following horizontal bounds:

X = -688, -432
Z = -1240, -984

Remember, any overworld portals within 1024 blocks of each other will link to the same nether portal, because 1024 blocks in the overworld = 128 blocks in the Nether, and the game checks for portals in a radius of 128 blocks.

If you build a new nether portal at the blaze farm and destroy your old portal, your main base portal will probably link up to your blaze farm. However, when you attempt to go back to the overworld, Minecraft will look for a portal within the above bounds and create a new one if it doesn't find one.

Your best option is probably to build a rail line from your current portal to the blaze farm. Ghasts can destroy any block with a blast resistance below 20.17, but they won't shoot at you without a line of sight, so you can make an inexpensive safety-tunnel around your rail line with pure Netherrack.

You can also build a more scenic tunnel with stone, glass, leaves, fences, etc, since Ghasts cannot "see" through transparent blocks.

Yes, you can. It's pretty simple, use the following code:

/tp @p[x=0,y=0,z=0,r=0] *tp coordinates*

Where the values x, y, z define the center of the search (the player nearest to these coordinates would get teleported) and r defines the radius of the search. If you don't want to limit the radius omit r.

Do not use decimal values for the search center, this will not work.

See here for more info.