What I have done with some 'very important' devices is do just that. Change the cron entry for specific entries to 1 minute.
Would this break anything Adam? These are smaller Cisco devices with few interfaces.
It won't do anything, because the RRD won't store more than one data point every 300 seconds.
If you changed the RRD databases, they'd stop storing the normal datapoints, because they would be at the wrong resolution.
Like I said, it can't currently be done.
You could change the entire installation to be 1-minute, change the RRD template and delete all of the existing RRDs, but you wouldn't want to, because that would be a lot of load on your network and on the observium host.
Also, your changes would likely be overwritten by a future update, then you'd be stuffed :)
adam.