This is a great idea @GregC and I haven’t seen much discussion here about tracking adjustments to the cost basis of your home.
One simple approach might be using a single tag for those transactions (perhaps with a name like 123 Hill Street Cost Basis).
Those investments (like big home improvement projects) or credits (like insurance payouts) might get categorized to different categories or groups over the years. That’s why using a tag for individual transactions rather than an entire category/group seems like the right move to ensure you capture every transaction that might be relevant.
If you tag each transaction that will be applicable to cost basis calculations at the time it arrives in your spreadsheet, later you can generate a Tags Report of all those tagged transactions and pass it along to your accountant for review.
Having worked in a tax firm before, if you roll in with that level of organization, you might be your CPA’s new favorite client! 
I know there are some financial professionals who pop in from time to time so I’m curious to hear of their recommendations on this too.
Edited to add: @martha.rudkin has a great solution above too!