Some people just want the house, so here's how to do so, even without my modifications.
Step 1: Access the Castle
Open up the console (hit `) and type
coc CLWCastleExt01
Go speak to Lahar at the front gate. Follow through normally until you get the key from Lamashtu.

Step 2: Repair the Pipes
After you retrieve the key, open up the console and type:
tgm
(Toggle God Mode, which gives you infinite health, stamina, and magika)
coc CLWNurndural01
killall

Open up the console and click on something in the world. Take the first two characters in the FormID (looks like a bunch of random letters and numbers) and replace the Pound symbols in the command below with them:
player.additem ##431799 10

From there, repair the pipe. Once you get 7 of them, you'll get quest markers. As soon as you've repaired all 10 sections of the pipe, type in the console:
coc CLWCastleMausoleum
(I didn't have you go back to the castle directly because there is a scene that must play out first. Trust me, I've tried.)

Follow through the quest normally, until Lahar tells you to get the heart from Nurndural.

Step 3: Get the Heart
Once Lahar tells you to get the heart, open up the console and type:
coc CLWNurndural01

Go to the music, listen to Amalgam, and go through the door. Once there, type:
killall

Then, wander around a bit until Almalgam wants you to get to him (there's a portcullis that opens there). Go find him, then start combat. Repeat the last command. Go find the lever base, then add the handle:
player.additem ##58B137 1
(replace those pound symbols the same way as before)

Activate the lever, then get the heart. Once you've done that, go back to the Castle:
coc CLWCastleMainHall

Follow through the quest like normal, until you have Lamashtu following you.

Step 4: Kill Shadow
Once Lamashtu is following you, type:
coc CLWNurndural04

Follow through until you get ready to find Shadow. Find Shadow in the very back-right (I had that as left for the longest time. facepalm). Once the sarcophagus opens up, do killall 3 times (hint: You can use the up arrow to auto-fill the previous command). Exhaust Lamashtu's dialogue, then use:
coc CLWCastleMainHall

Complete quest normally.

NOTE: If you still have God Mode enabled, you can toggle it off with
tgm

You now own Clockwork Castle and HAVEN'T broken anything!