But the Tempest and P-47 were pressed into those roles?
Mainly the Typhoon rather than Tempest.
The pilots were trained in ground attack methods. RAF pilots, already qualified and at operational squadrons undertook a three week course.
Fighter pilots' lives were not squandered flying CAS, interdiction and armed reconnaissance missions. This was a role which had been anticipated much earlier when a decision was taken about what sort of aircraft would operate in support of ground forces. In the case of the USAAF a meeting was held at Wright Field in March 1943 to discuss whether to use fighters (what we now call fighter bombers) or dive bombers to provide air support for ground forced. The principal reason for choosing the former was that they would be able to defend themselves against hostile fighters.
The British had arrived at the same conclusion much earlier. This followed their own experiences on the offensive in France and the defensive during the Battle of Britain. Initially the British rated the Ju 87 very highly but it's operational limitations were exposed during the BoB. This simply reinforced the cultural prejudice of the junior service when asked to operate in support of the army.
The Hurricane IIA (12 x .303 MGs) and IIB (4 x 20mm cannon) appeared in 1941 and later that year Nos 1 and 3 Squadrons were flying intruder missions across the Channel with their IIBs.
Tactics for this sort of mission were developed in the summer of 1941 by the Air Fighting Development Unit. The first real fighter bomber attack was arguably carried out by "Hurribombers" of No 607 Squadron who bombed an electrical transformer at Tingry on 30th October 1941.
It is quite wrong to say that aircraft like the Typhoon were pressed into service in the fighter bomber role. It was a role anticipated before they even entered service. Tests with bombs and rocket rails were carried out long before the Typhoon entered series production and relevant revisions made by Hawker. Humble flew DN340 on 17th March 1943 with two 1000 lb bombs and an all up weight of 13,248 lbs! He managed to dive at 548 mph TAS before releasing the bombs.
Cheers
Steve
Edit: for the Brits Bill Humble, Hawker test pilot, was the rather delectable Kate Humble's grandfather.
She doesn't look like that "down on the farm!"