I believe so. I tried that here by just uploading the entire system and deleting everything I didn't need but the only frequencies that showed up were the ones I already had programmed
For a large statewide, or regional system, such as NTIRN in our area, you can selectively append one or more specific departments if you do that properly. But while you can restrict your append to only the department(s) that you want, Sentinel still appends
all of the sites on the system. You have several choices on how to proceed if you really don't need, or want, the excess baggage of extra sites.
Some people prefer to leave them in place, but restrict which ones are actually not needed (or wanted) by setting that Favorites list to use location control. If you do that, then the out of range sites will be ignored; at least until you either change your location & range settings, or connect a GPS preparatory to taking a trip. You can also wade through the excess sites, and manually set the extras to "Avoid". I prefer to simply delete the ones I don't need; get them out of the way to reduce clutter when I need to make a change to that list at a later date.
Now, presuming that you did delete what you did not want, but now need to add some of it back, or add an additional site and/or departments, Sentinel does not readily let you do that. It 'remembers' that once upon a time, it appended everything, so when you go back to try & add something deleted previously, Sentinel resists that.
The key is that if the name of your system in your list, is the same as the name when you first appended sites & departments to a list, then Sentinel will resist doing what you intend to do. But there is a simple work-around. Change the name of the system, in your Favorites list, to something other than the same name as when first appended, Do that in the Favorites list editor. Then save the changes & return to Sentinel's initial screen. Now, you can go into the database files, & append the system to your list. Sentinel, not seeing the same name, will append all the sites again, as well as any departments selected.
Now, go back to edit your list. You'll have the system in there twice- the renamed system from your first append, along with the system as it is in the database, with the original name. In the Favorites list editor, you can copy & paste whatever sites, or departments, you want into the original (renamed) system on your Favorites list. Then, once you've done that, you can delete the most recent append, and, if desired, revert the name of the system back to the original.
Of course, since you are a Premium Subscriber, you can simply use software such as
ProScan to import what you need without the gymnastics needed to do this solely within Sentinel.
If you want a copy of my modified Northeast Tarrant list, which is broken out by city & departments instead of one huge department, send me a message & I'll send it to you. Click on the envelope in the upper right corner of the page & start a new conversation. Here's a sample of what the system looks like in my scanners: