Many config files in users home directory just override/add to ones in the /etc - for example the settings for GIMP in the users home are in ~/.gimp-2.*, which adds to the system-wide config /etc/gimp/2.0.

So for ~/.bashrc, you could edit the system wide config files /etc/bash.bashrc (for functions/aliases) or /etc/profile (for environment stuff) - you can the full list from man bash:

FILES

       /bin/bash

              The bash executable

       /etc/profile

              The systemwide initialization file, executed for login shells

       /etc/bash.bash_logout

              The systemwide login shell cleanup file, executed when a login shell exits

       ~/.bash_profile

              The personal initialization file, executed for login shells

       ~/.bashrc

              The individual per-interactive-shell startup file

       ~/.bash_logout

              The individual login shell cleanup file, executed when a login shell exits

       ~/.inputrc

              Individual readline initialization file

This warning is given for a few Linux systems in the files:

# It's NOT a good idea to change this file unless you know what you

# are doing. It's much better to create a custom.sh shell script in

# /etc/profile.d/ to make custom changes to your environment, as this

# will prevent the need for merging in future updates.

So you could edit those files, you may want to back them up first (cp /etc/bash.bashrc /etc/bash.bashrc-backup for example), or create a shell script in /etc/profile.d - for example you can create one with these commands (with sudo/as root):

touch /etc/profile.d/custom.sh

chmod +x /etc/profile.d/custom.sh

Then open it with nano /etc/profile.d/custom.sh

#!/bin/sh

alias ls='ls -lah'

And check whether it works by seeing if it appears in the output of alias - Note that you may need to logout/login or reboot to see any changes (if you don't want to, running source /etc/profile after any changes might work)