Blocking notification based on content or sticky-ness I have a messaging app (TextNow) that sometimes likes to put a sticky notification up (to notify me that I have used up my data and am being throttled), which I do not want and cannot be disabled in the apps settings. 

Normally when an app abuses notifications like this I simply disable notifications for that app. However, in this case I would miss text messages if I did that. Therefor I was hoping for some way to either:


Block notifications based on their content.
For this specific app, only allow dismissable notifications.


I do have a rooted phone.

Example of the notification:



Note: I have posted an answer to this question, but I am still looking for better options.
automation is  preferred option, since OP is looking for context based actions . Many apps are available. I prefer using MacroDroid,  since it is free (upto 5 macros) and easy to learn (app guides you through the settings - make sure from the app settings you activate ignore battery optimisations if using Marshmallow)
OP has confirmed in his answer that Macrodroid approach as suggested by me in comments worked and his answer covers another automation app as well
You would need two macros for this to start with ( needs root)
First macro would look like this (Triggers / Actions / Constraints are added by +)
Macro 1 :  Remove notification (name of macro )
Trigger : Notification → Notification Received → Select Application → Choose App → Text Content → Contains (Notification Text which you wish to disable)
Actions:
Configure App Notifications → Choose App →Disable
Constraints:  No Constraints
Logic: We need to identify  the content of notification  to disable this notification from appearing. Not specifying any Constraints means we want the macro to always run
In the next macro, we make sure that if the content of notification is anything else, that notification is shown
Macro 2 :  Enable notification (name of macro )
Trigger : Notification → Notification Received → Select Application → Choose App → Text Content → Excludes (Notification Text which was disabled in earlier macro)
Actions:
Configure App Notifications → Choose App →Enable
Note:

Tested and working on Moto X Play, Android 6.0.1, with a different app, since app in OP doesn't work in country

In my experience, heavily modded OS's  like Samsung, Huawei, MIUI at times produce unexpected results, so it is better to have two separate macros - easier to troubleshoot from the app logs.


Optimal approach
Once you have them working satisfactorily, you can elegantly combine above macros to have a single macro (not tested by me since I don't have any apps that produce multiple sticky notifications but should work). This is a better approach, since notifications aren't lost as pointed out by OP in his solution

This will dismiss any other notifications that also happen to open from the same app at the same time.

Macro  : Enable / Disable notification selectively
Trigger : Notification → Notification Received → Select Application → Choose App → Text Content → Any
Actions:
If Clause → Add Condition →Notification Present → Select Application* → Choose App → Text Content → Matches ( Notification Text for which you wish to disable )

Add Child action ( by long press of above action) of first Macro

Add else clause ( long press if) and add action of second Macro