AIUI, the pilot having a CPL modifies the scenario under discussion only in that he can now be contractually required to fly, in other words he can be a paid company pilot.
And this is true for both a JAA CPL and an FAA CPL.
This is widely relied on, in both G-reg and N-reg corporate jet operations which employ both CPL/IR and ATPL pilots.
Having a CPL doesn't AIUI modify the [in]ability to conduct "aerial work", practically all of which requires the operator to have an AOC. This is incidentally also true in FAA land, although they allow a bit more latitude. The CAA requires an AOC for just about everything of relevance.
A CPL allows one or two other trivial things; I vaguely recall it enhances the radius with charity flights, or something like that.......
But if it's your personal aircraft, you've got to find a way, if you want to, to include things like financing, depreciation, annuals etc into the "direct" costs of flying. For instance by going through an intermediairy company
I don't believe you need to work through another company to do this, although doing so certainly clarifies the matter. IMV "direct costs" does include
fuel
landing fees
engine fund
prop fund
any hours-based maintenance
depreciation
but does not include
annual maintenance
finance costs (other than a possible airborne time related element)
If you work the supply of the plane through a company then everything can be included, and this is exactly what happens when you rent a plane from a school - they are billing you for the lot, plus a profit margin.
I wrote to the CAA about this some years ago, because I was operating a plane through a limited company, of which I was also a director, and I was concerned that I could potentially bust the PPL cost sharing rule, by charging 3 passengers 75% of the direct costs while also drawing a salary from the company. Their legal dept said it was OK - unsuprisingly, otherwise any employee of a flying school would not be able to use the PPL cost sharing scheme to the full.