Remmina - The GTK+ Remote Desktop Client  v1.4.33
Remmina is a remote desktop client written in GTK+, aiming to be useful for system administrators and travellers, who need to work with lots of remote computers in front of either large monitors or tiny netbooks. Remmina supports multiple network protocols in an integrated and consistent user interface. Currently RDP, VNC, NX, XDMCP and SSH are supported.
Connect to multiple profiles from a terminal
╭─antenore@bigmom /data/remmina/profiles
╰─$ remmina -c barfoo.remmina -c foobar.remmina

Edit settings of existing profiles

╭─antenore@bigmom /data/remmina/profiles
╰─$ cp test-spice_spice_ubu20_192-168-1-39.remmina test-spice_spice_ubu20_192-168-1-28.remmina
╭─antenore@bigmom /data/remmina/profiles
╰─$ remmina --set-option server=192.168.1.28 --update-profile test-spice_spice_ubu20_192-168-1-28.remmina
╭─antenore@bigmom /data/remmina/profiles
╰─$ diff test-spice_spice_ubu20_192-168-1-28.remmina test-spice_spice_ubu20_192-168-1-39.remmina
8c8
< server=192.168.1.28
---
> server=192.168.1.39

--set-option can be used multiple times and the last one must be followed by --update-profile and the connection profile file (.remmina)

Encrypt a password

$ echo foopass | remmina --encrypt-password test-spice_spice_ubu20_192-168-1-28.remmina
Enter the password you want to encrypt:
Encrypted password: G1/IJfT3evw=
Usage:
rdp://username:G1/IJfT3evw=@server
vnc://username:G1/IJfT3evw=@server
vnc://server?VncUsername=user\&VncPassword=G1%2FIJfT3evw%3D

This is the password using the default Remmina password encryption algorithm, but consider that is not safe.

If you want to be safe, use kwallet or gnome-keyring, in the password field use a . (dot) and search how to add secrets from the command line in kwallet or gnome-keyring