Thanks for the solution! Maybe, a 'Restart application' button (admin area) should also rewrite Global.asax file (just open and save without changes). It'll allow store owner to do it in admin area without any manual work.
Yes, this will be very useful especially for normal users(not developers) as they will probably not have access to their Global.asax file.
Actually they shouldn't even care that such file exists :)
They just want to drop a plugin(or even better if they could upload a .zip file with the plugin via the administration panel), install it and start using it.