Actually, this is currently possible by changing this file in recent Lansweeper versions: Lansweeper\Website\js\chartjs-helpers.js. After changing it, do a Ctrl + F5 on the website to refresh the javascript
Change at your own risk, and the file will probably get overwritten during upgrades though. This was added when Lansweeper changed its plugin used for chart creation, not too long ago, which should also have fixed visual bugs like text not showing properly and the colours not matching.