I am currently learning how to manipulate the OOTB MvParts to show how our company requires diffusers to appear on our drawings. I have written this up using a diffuser as an example. You will have to modify the paths shown to get to where you are storing your MvParts.
MvPart: How to Change the Top View Representation:
This is to copy an existing MvPart and modify the "Top" view of it.
In this example I will step through modifying a diffuser.
Open a completely blank drawing based off of your template.
Go to modelspace.
Go to CAD Manager/Content Editing/Catalog Editor.
On the pop-up go to File/Open/ X:\enu\Aecb Catalogs\MvParts US Imperial\Mechanical\Mechanical MvParts US Imperial.apc (at the very end of the list) and double click on this to open it.
Go to the desired section; in this case: Air terminals/Diffusers
Select a diffuser, right click on it, and click on "copy".
Click on the Diffuser subcategory, right click, select "paste".
Now you have a copy of the original diffuser.
Right click on the new copy, select "rename" and rename the item.
Put your company initials in the name to designate that it is a company modified part now.
On the right hand side click on "Description" and change the information there to match the new name you gave it.
Go to File/Save, to save the drawing.
Close out of the pop-up window.
Now double click on the Catalog icon (magenta colored book looking icon) at the bottom of the screen located next to the padlock icon.
This is to regenerate the catalog to include the new part you have added to the catalog.
At the command prompt it will ask for input, type "m" for MvPart as the catalog you want it to regenerate.
You will see a progress bar for the regeneration process.
Click "ok" on the pop-up warning. (if it shows up after regeneration)
Do not go through the Content Builder to make the top view changes.
Go to File/Open/ X:\enu\Aecb Catalogs\MvParts US Imperial\Mechanical\Air terminals\Diffusers
Open up the new .dwg you had created with your company name in it.
Type "be" on the command prompt to open the block editor.
Scroll down to the desired view. In this case you are looking for the TOP view drawing.
There will probably be multiple blocks with "TOP" in the name.
You will probably want to modify all of these so you have the correct symbology on all of the different sized diffusers.
Eventually you may want to change the blocks with "SYMBOL" in them as well since these are the blocks used for symbolic representations for 1-line and other drafting.
Edit the block(s) as desired to reflect what you want to see in your drawings.
Save the block(s).
Save the file containing the block(s).
Use the Mechanical Equipment icon on the Duct palette to access the diffuser you just changed.
(Or whatever other icon you use to access MvParts)
Set the "Part" tab as active.
Surf down to: All Installed MvParts US Imperial/Mechanical/Air Terminals/Diffusers/ and choose the part that you added/modified (should have your company name in it).
Drop the part into your drawing and verify that it looks like and acts like you need it to.