What type of encryption did you use? If it’s full encryption, the entire VMX file is encrypted. You’ll need to decrypt the VM before editing the VMX file manually.
With the partial encryption options (the Fusion 13 partial encryption and the broken Fusion 12 experimental encryption) the VMX file is not encrypted (there are individual entries that look like they might contain encrypted data but don’t touch them). You can edit the file manually after you’ve shut down the VM and Fusion.