So what to do in a situation like that when you are invited to play a recital or church service on a historical organ, or maybe you are just visiting the church which houses such an instrument and are given an opportunity to try it out?
Here you must remember this rule - organ playing is like driving a car. At first, when you have just taken the driving exam and got your driving license, you are used to driving just one car only (most of the time).
Can you remember the feeling when you tried to drive the second car? It took a while to adjust to it - breaks work differently, gear shift and clutch (if your car has them) work differently as well. In other words, every little detail about the new car might be different. Perhaps not totally different but just a little. And sometimes the adjustment process takes up to a week or more.
But later in your driving experience you begin to get exposed to different cars and little by little your driving experience increases. Consequently, the time required to adjust to a new car decreases. Most of the people, though don't drive many cars all the time, only the professionals do. So the true professionals can adjust to a new car in no time.
Likewise, playing different organs is also similar to driving a car. The more organs you have visited and played, the faster and easier will be to adjust to uncomfortable instruments.
I remember back in 2000 when I participated in Gothenburg International Organ Academy (Sweden) they had a few very significant instruments built in the 17th century North German style. One was in the famous Orgryte New church - a 4 manual organ in the Schnitger style. The second - a 2 manual organ by built by John Brombough in Haga church. They also had pedal clavichords available for practice.
These organs had split keys - the so-called subsemitones. In other word, E flat and D sharp was not the same (as there were several others on each keyboard). As you can imagine playing such an organ is no easy thing for an organist with little experience on historical organs.
So let me tell you this - I felt miserable, not only I had trouble figuring out which split key belonged to which note (the more common ones are in the front, but I didn't understand that at first), I also felt quite incapable of playing them without mistakes - especially the Haga church organ because the action was so light and the size of the keys was smaller, especially on the 2nd manual. Evidently you need to know early fingering in order to play such instruments.
By the way, I played Buxtehude's Praeludium in E major on this organ. For a person with no experience with split keys it was a very foolish idea because of number of sharps.
But later in life, when I got much wider exposure to historical organs through my studies, I returned to Haga church in 2011 to play a recital of Renaissance motet intabulations. Now the feeling was quite different - I felt at home with this beautiful organ. I prepared all the registrations in advance at home so when I was given 2 hours to practice, I felt I was ready after just 30 minutes. So the rest of the rehearsal I just improvised and enjoyed the instrument and its marvelous sounds. There was no feeling of stress or anxiety when one has to face an uncomfortable organ.
What can you learn from this story? The main point is this: as with driving a car - the more organs you have played, the easier it will be for you to adjust to them.
By the way, do you want to learn my special powerful techniques which help me to master any piece of organ music up to 10 times faster? If so, download my video Organ Practice Guide.