A spring will only permanently change shape if it is compressed or stretched beyond its designed limits, or if the spring is of poor quality or not suited to the job it performs. Magazine springs are designed to be compressed as far a fully loaded magazine compresses them, and the follower usually is designed to prevent the magazine from being overloaded.

Springs will wear out over time, but the high quality springs used in defensive handgun magazines will likely take thousands of compression cycles before they wear out.

Go ahead and top up those H&K mags and don't worry about them. They'll be fine. I keep my Glock 21's mags fully loaded all the times unless I'm travelling to and from the range (fricken liberal carry and transport laws don't allow otherwise). And I've never had any problems with magazine related stoppages.

Mike