The most common are overfueling, while others include adding alcohol or LP gas injection, and turbo-charging naturally aspirated engines. These all sound tempting when an operator is faced with covering more acres in less time. The first problem is warranty. Most manufacturers do not allow any changes from standard specifications without voiding the warranty, so you're on your own with the changes. The second problem with engine modifications is an almost sure reduction in service life.
Every machine design is a compromise.
The designer must compromise between strength, reliability and cost to come up with a tractor rugged enough to do a job, but still meet an affordable price. Tractors are designed to operate at different travel speeds, but the final drives are not designed for all possible torques theoretically available. If power is increased 20 percent on a tractor, you're assuming the manufacturer built the engine parts, clutch, transmission and final drive 20 percent stronger than originally needed. Speed also has an effect on service life. For the example just stated, the 20 percent increase of power could be used by keeping the tractor weight the same and travel faster.