Difference between Retention preiod and Rentention level

Level  Days  Label
   0       7  1 week
   1      14  2 weeks
   2      21  3 weeks
   3      31  1 month
   4      62  2 months
   5      93  3 months
   6     186  6 months
   7     279  9 months
   8     365  1 year
   9   24855  infinity
  10   24855  infinity

Look at aboveIf you got custom requirement to keep backup sets lets say 5 Days or 45 days

You can select level 10 from master server host properties and you get option to change it from infinity to either 5 days or 45 days... 

So above would look like

8     365  1 year
9   24855  infinity
10   5  days

So if your regulator says retain data for this application for 3 yrs or 5 yrs or 7-10 yrs... you indeed can  simply by changing any of retention level (10 onwards  ... do not overwrite any existing customized retention periods if already done) and set it to 3/5/7/10 yrs whatever your requirements are.

Although you can extend image retention using CLI however it ain't way to follow practise unless needed.

Hope above clears