To answer your question, we need to make a distinction between two different types of passwords:
- Spectre-generated passwords,
- Custom passwords (passwords you made yourself or were made by another app).
If you add a site to Spectre, by default it will set the type to "Long", which will give you a long Spectre-generated password for the site. This type of password depends on your login name and your Spectre secret. If you change either of these, the password Spectre generates for the site will change.
However, you can also set the password type for a site to "Own" (aka "Personal"), which will allow you to save a password into the app (encrypted with your Spectre key), that came from elsewhere. In this manner, you can import old passwords into a new Spectre user.
With that said, my recommendation for your security is to default to Spectre's own generated passwords and rather than importing old passwords, change the old passwords in your accounts to the new one generated by Spectre. It will ensure that you have high-quality passwords which cannot be lost in any event.