I'm late to responding, but my understanding is that MA's "Convenience of the Employer" rule was put in place specifically for the pandemic and is effective until mid-September 2021. I have known folks who worked in MA and worked remotely in NH or other states on a regular weekly basis, who would apportion their income. I would think if you work for the state of MA, they can opine that you worked remotely one day a week before the pandemic at your NH home. This would allow you to apportion your income. See a couple of links to articles I have posted below.
https://milestonefinancialplanning.com/blog/live-in-nh-but-work-in-ma-what-to-know-about-your-state-...
https://www.pewtrusts.org/en/research-and-analysis/blogs/stateline/2020/10/02/remote-work-boom-compl...
https://www.mass.gov/directive/directive-21-1-personal-income-tax-guidance-for-employees-who-telecom... (This is state guidance. See Section III. Directives)
