It can be done. You have to edit the db_countries.lua under \DCS world\scritps\Database
Under
-- ISRAEL
local units = {}
copyTable(units,db.default_units)
*** Add the line (under the planes section)
cnt_unit( units.Planes.Plane, "Su-25T");
For specific skins you would need to edit the description.lua file for the specific skin that you want under \DCS World\Bazar\Liveries\SU-25T
Add "ISR", in the list of countries.