This is actually a suggestion for support to add this to help.
You can disable fill by right clicking the fill icon to turn off, or pause, fill.
Hello @rheitzman,
My name is Henry and I am happy to assist with your inquiry, and appreciate you contacting LastPass Support!
Thank you for your suggestion. There is already an option that allows you to do this. Please see the following article.
Please let me know if this worked or if further assistance is required.
Thank you,
Henry | Customer Care