Hello!
Recently I find more people asking how they can extract CE maps, and rebuild them into MCC. I want to state that this is possible; however, the modding community does not, and never will, condone ripping others' work. This should only be done for maps you have made in the past, maps you have gotten permission from the author, or maps used only for personal use. As far as the "preservation of modding history." discussion; I will refrain from discussion here. This is a moral grey area, and it's an issue the community will have to figure out. 
Lets do the thing!
  We're going to be utilizing invader, and the anniversary HEK for this.      Step 1: Setting Up The Tools
Starting off we need to install the Halo CE Modding Tools tool in steam. This link should take you right to it. ( for some reason OC doesn't seem to like this link: steam://run/1532190 paste into URL to open steam )
After this we need to download Invader, and install it into the Chelan_1 directory. ( It is a 7z archive, I use Win-Rar, but you can use any archive software really )
From here we want to navigate to the MCC Modding directory that steam made for us called Chelan_1. An easy way to do this in to click on the cog in the steam page for the modding tools.   If you're having trouble locating the editing kit in your library, make sure you have "tools" enabled in the library filters. 

There will be three zip files inside Chelan 1. data, shaders, and tags. You'll want to extract each of these into the modding directory.

Keep in mind that with the recent season 8 update there have been changes to some tags. if you have already extracted these folders, you may want to re-extract them to keep them up-to-date. You may experience HUD issues. With all of that out of the way, we should be all set to move on to the next step.
Step 2: Extracting Tags I personally don't have any maps, or tags to port over currently. For this example I'm going to use the classic map Yoyorast Island. Remember we don't condone ripping others' work. This is just for an example. 
I'm going to install the map in the maps directory in the modding directory. ( note if it doesn't exist, just create a new folder and name it maps )

  Back in the root directory of the modding folder, we're going to open a command prompt by typing in the folder URL bar "cmd"
  After we do this it will open a command prompt that is already opened in this folder.   If you just have a tags folder to transfer over, copy the new tags into the tags directory, and go straight to step 3 from here.   Next we're going to use invader-extract to...well.. extract the map. The only arguments that are needed is the exe ( yellow ) and the map we're extracting ( green )
It will print a bunch of text to the console showing the process of the extraction. Skipped tags are tags that already exist in the tags directory. ( you can over ride this if you like but it is not recommended. )
And once it finished you have finished with the extraction of the tags. You'll get a confirmation at the end ( I extracted none, because I already extracted them once before practicing for the tutorial. ) Don't close the command prompt, as we will need it in the next step.
  Step 3: Cleaning Up The Extracted Tags Lastly we need to do some clean up to the tags, as some of the tags for CE have invalid data for MCC. Invader makes this step simple as well, we're just going to run two commands. "Invader-bludgeon --all", and "invader-strip --all"

Invader bludgeon is going to go through all the tags in the tags directory and sanity check them. It will attempt to fix any issues noticed. Keep your eyes out for any red entries, as these may require manual fixing. This typically is caused by tags extracted with really old tools like HEK+ that screwed up the tags so badly that invader can't assume the fix. I have found a few shaders like this.
Once that finishes you'll get a confirmation, like with invader-extract.
  After we're going to run "invader-strip --all"
This is going to strip hidden data from tags and recalculates their checksums. This is needed for MCC to not think the tags are corrupted.

  This will take a few mins to run through as it has to do this to every tag. Once it finished though the tags should  be in a usable state for MCC. We can attempt to open the scenario inside of Sapien to verify that claim.



Stonks, and for the icing on the cake, we'll build the map, and load it up in game:



There are going to be many issues you run into. Feel free to comment down below and I will be happy to answer any questions. Any common issues ill add to the end here in a trouble shooting section