One of my opponents at correspondence chess (CC) recently apologised for taking longer than usual to make move six in a Caro-Kann Defence as White, saying that he used CC games to “investigate lines for use over the board (OTB)”. My opponent is a strong county player whose OTB grading is the equivalent of around 2100 FIDE and I know that he has faced OTB GM opposition in the past. I was very pleased to hear this, as often OTB players dismiss CC altogether.
So how can this help? Well, for a start, your OTB grading will not suffer, only, perhaps, your CC grading assuming the games are actually graded. Your opponents will not know what you are analysing until you have it all prepared. A CC game is a good test for a new move, as you and your opponent can look much deeper into the position than in an OTB game. I also know that there are some strong OTB players who consult computer programs for analysing games and future lines that they will play. However, even the best programs can make mistakes in difficult endgames, so you really need to check out every move yourself to be sure.
There is another way as well. You can enter a CC thematic tournament where the opening is already chosen and you start the game from a certain position. Often you will play two games from the same position with each colour against the same opponent. The games are not usually graded so there is no fear about losing points. Of course, it needs to be an opening you have an interest in! Typical openings are the Dutch Defence 1d4 f5; Larsen Opening 1b3; Benko Gambit 1d4 Nf6 2c4 c5 3d5 b5 4cxb5 a6 5bxa6; Sicilian Portsmouth Gambit 1e4 c5 2Nf3 Nc6 3b4. I once played in a Latvian Gambit tournament, but seem to have mislaid the games…
So, if you are purely an over-the-board player, why not try correspondence chess or, better still, the modern version called webserver chess to explore your openings!