Are there any single-player cheats for OFP?

Yes, there are a few but if you're looking for an invincible god mode cheat - sorry - there isn't one. Besides, God doesn't cheat.

The following cheats are built into OFP by BIS and do not trigger FADE:

Hold the left SHIFT key and press the MINUS ("-") key on your keyboard's numeric keypad. Once you have done so, type in one of the following codes to activate the respective cheat:

savegame - Type during gameplay. This will save your game's retry position. Each time you save your retry position, your previous retry position will be overwritten. For other alternatives to performing multiple saves, read this FAQ item.

endmission - Type during gameplay. This will let you end your mission before completion and, in a campaign, will let you continue to the next mission. All this comes at a price, however.

campaign - Type during the main menu. This will display all the missions in a campaign and let you play them out of sequence as individual single player missions.

topography - (From OFP: Resistance version 1.75 and above, you must play with a TERRAIN DETAIL setting of VERY LOW for this to work). This isn't a cheat but you might appreciate the results. Type during gameplay or while in the mission editor. This will create a file in your hard drive's root directory, named island_name.emf, containing a vector representation of the map of the island on which you are currently playing or editing. Note: these files are very large.