I have tried to deal with similar issues and I don't think just changing the DPI value to 200 will work -- modern linux distributions seem to work nicely on HiDPI (and they seem to detect when to do so), it seems they tend to arrive there by working around X11's idea of DPI (for instance, for gnome the magic seems to be gsettings set org.gnome.desktop.interface scaling-factor 2), and for some legacy applications I haven't found a way to fix them (certainly, anything depending on bitmap fonts seems out of luck). For instance, for maple's graphical interface I have found the accessibility "Desktop Zoom" the only reasonable option (Super+Alt 8 in Gnome -- if you set the mouse to "push" rather than "center" it's actually pretty usable).
I have tried to deal with similar issues and I don't think just changing the DPI value to 200 will work -- modern linux distributions seem to work nicely on HiDPI (and they seem to detect when to do so), it seems they tend to arrive there by working around X11's idea of DPI (for instance, for gnome the magic seems to be gsettings set org.gnome.desktop.interface scaling-factor 2), and for some legacy applications I haven't found a way to fix them (certainly, anything depending on bitmap fonts seems out of luck). For instance, for maple's graphical interface I have found the accessibility "Desktop Zoom" the only reasonable option (Super+Alt 8 in Gnome -- if you set the mouse to "push" rather than "center" it's actually pretty usable).