Lombard,
If you want more runs then you shall have more runs.
I’d recommend each week alternate between dropping an easy swim and then the following week a hard swim, so you just doing 2 swims a week.
You can for sure add more running, it just needs to be a) added with the 80/20 ratio and b) no more than 20% more running volume than recently completed.
Therefore, if you ran a maximum of 3.5 hours in the past 4 weeks, you can add an additional 40 minutes (20% of 3.5) without risk. That 40 minutes should be close to the 80/20 ratios, so 8 minutes hard, 32 minutes easy. You can do the whole additional run easy as well.
David