Is it possible to apply vim configurations without restarting?

Yes, just use the :so % command while editing your .vimrc.

If you want vim to auto-reload your configuration, you must add the following commands :

augroup myvimrchooks
    au!
    autocmd bufwritepost .vimrc source $MYVIMRC
augroup END

the grouping of autocommand is here to avoid "exponential" reloading if you save several times your configuration.

Here's a more cross-platform compatible version if you run on Mac/Windows/Linux and gvimrc:

augroup myvimrc
    au!
    au BufWritePost .vimrc,_vimrc,vimrc,.gvimrc,_gvimrc,gvimrc so $MYVIMRC | if has('gui_running') | so $MYGVIMRC | endif
augroup END

The autocmd watches all potential *vimrc files and when one changes, it reloads the vimrc file followed by gvimrc if the GUI is running.