Set change and changing / refilling the reservoir and tubing are two completely different things. You should change the set every 3 days max, but you can change the reservoir whenever you want, just wait until the insulin has run out! Same for the tubing, change with the reservoir if you prefer. Only caveat is that if you take longer than a week to use a full reservoir, you should probably change it then to be on the safe side (in practice it’s fine, but there are some issues about insulin deterioration after a week or so in the reservoir).
As for the Medtronic sets, try the Silhouette sets. No auto-inserter needed, and they’re actually far less prone to problem than the auto-inserted sets such as QuickSets. Furthermore, if you want to use non-Medtronic sets (ie those with a luer Lock) with a Medtronic pump, you can get a converter. The only issue may be persuading your CCG to fund you supplies from two different manufacturers, depending how picky they are about such things. But in this case you just need to give them evidence of why you need to do so.