It's not possible

To the best of my knowledge it's not possible. Updated applications are supposed to query global settings for HDPI (High Dots Per Inch) and behave accordingly.

Work around with xrandr

Luckily (or unluckily) some applications do not query the global settings in Unity Tweak Tools (or in your case Gnome Tweak Tools) and their settings depending on xrandr instead.

Take for example kid3 which ignores global settings by the tweaking tools. When started it looks like this:

If you open the terminal first and use:

xrandr --dpi 144

then call kid3 the screen is magnified and easier to read:

Work around with Zoom

Within applications like LibreOffice and Google Chrome you can zoom in and zoom out to adjust HDPI to your liking.

For example in Chrome you can use Ctrl++ to zoom in and Ctrl+- to zoom out for an individual tab.

Additionally in Chrome you set the global page zooming factor in system settings:

Notice the last option sets Page Zoom to 110%.

Generally speaking then you can solve most HDPI issues on an application by application basis but not within tweaking tools.

17" laptop at 1920x1080

On my 17" 1920x1080 laptop screen I use tweaking tools to set font scaling to 1.5:

In Ubuntu System Settings -> Screen Display I set monitor scaling to:

I spent a lot of time getting my settings just right for me with the laptop 3 feet away. I expect you and others might also have to invest considerable time too.

There are other issues to consider such as icon size in Desktop and Nautilus which you can also experiment with.