Depending on the siding something like blown in cellulose insulation can be installed with removing the siding.
With wood siding holes can be bored and plugged afterward..... refinsh the area with paint or stain.
Vinyl siding is generally easy to remove sections to bore holes for the blowing in the insulation..... afterward the holes are plugged and the vinyl sections reapplied.
There is also the option of having holes bored in the interior walls which are plugged and minor patching and painting required.
Hope tis helps.
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