Can our organization make adjustments to the details (e.g. logistics) about a need, even at the last minute, and communicate the changes to all individuals who’ve signed up?

Yes, quantity needed, dates and times, descriptions of the need, etc. may all be changed and any time. The new details are reflected instantly on all web sites where a need appears. The content of reminder emails also automatically changes.  You can also email all individuals in each shift where a change has occurred.