There are a lot of users who want to customize their template system definitions for pipes and ducts in ACAD MEP. I have written a blog on "How to create a new Layer Style Key" this one will cover how to create a custom system style.
In ACAD MEP go to the Manage tab and open the Style Manager from the Style & Display panel.
For this purpose I will show how to do this within the Piping Objects but this can be done on the other objects as well.
In the Style Manager dialog box expand Piping Objects and expand Pipe System Definitions.
You can certainly change just the names of the Pipe System Definitions if you are ok with the layer that they are on. It is very important that you do not overwrite the out of box system definition until you have thoroughly tested your system definitions in the drawing to verify they all work correctly.
To make a copy of the pipe system definition select on the name > right click copy. Then right click again and paste. Your copy will have the same name but a number in brackets behind it such as (2) to indicate that it's the second one with this name.
Select on the copy and right click > and select rename. Now if you look at the two their settings are similar just the name is different.
Go to the Design Rules tab to start customizing the properties of your new system.
Abbreviation - If you are going to tag your systems and do not want the long name of the definition to show you will want to have an abbreviation. This can be whatever you want it to be.
System Groups - If you want different systems to be able to connect into one another you can put them on the same system. If you leave this portion blank then this system will be able to connect into any groups.
Layer Key - you can leave the layer key where it is or if you created your own layer key and have applied it correctly to your template, then you should see your layer key in the drop-down list. It is very important to create your custom layers before you change or create new system definitions. Also a very important key factor is that you have to follow the layer key system. So the M-SY-PIPE, if this is not correct you will not see your layer in this drop down list no matter how many times you assign your drawing or template to use your custom layer keys.
When you are done setting up your design rules, click on the Single Line Graphics tab and set or turn off by unchecking your single line displays. This is for pipe that you want to show as a single line if it is under a certain size. If this is on and is not set correctly users will think there is something wrong with their system or with their drawing because all their work is showing up as single lines. If you are not sure its best to just uncheck both of these.
Click the Apply button and ok to get out of the Style Manager. You will want to save this in a template or a master drawing where this will be safe from being changed. Refer to my blog mentioned above to learn how to set a dwg or a dwt as your layer key.
Test your pipe system and verify if the pipe and the elbows are all correct and on the same system and that your layer that is associated looks correct as well. Utilize your properties to change your system type, routing preferences, pipe size, elevation, justification and label settings.