Hello @johnlloyd_13 ,
it should be safe you just need to use recent client software for Putty or SecureCRT that support SSH version 2 that is considered more secure.
When you do the test do not close the original vty session and try to open an additional window to verify the new settings and the ability to access the device.
Hope to help
It is safe but you must fulfill requirements as ssh client must be updated that can support all required encryption algorithms.
router#show ip ssh
SSH Enabled - version 2.0 Authentication methods:publickey,keyboard-interactive,password Authentication Publickey Algorithms:x509v3-ssh-rsa,ssh-rsa Hostkey Algorithms:x509v3-ssh-rsa,ssh-rsa Encryption Algorithms:aes128-ctr,aes192-ctr,aes256-ctr MAC Algorithms:hmac-sha2-256,hmac-sha2-512,hmac-sha1,hmac-sha1-96
KEX Algorithms:diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1 Authentication timeout: 120 secs; Authentication retries: 3 Minimum expected Diffie Hellman key size : 2048 bits
To see what algorithms your device(s) support. Make sure one of these is listed in the SSH client you are using. More than likely it is, but can't hurt to check.
No it won't lock you out of your current session or future session from any terminal emulation software but it could for future ssh sessions between network devices - such has switch to switch or router etc..running different versions
One thing i am aware of from very recently is if you change
the the ssh authentication/mac algorithms then that can and does lock you out of future sessions from switch to switch or router etc but again not from any terminal emulation software