The answer to that depends on what device you have. You'll have to post again with at least that much information before we can answer.
In general though, the bootloader is something you can't edit, and certainly won't be able to modify without rooting your device. Our forums here have sections for different devices, and each has a subsection "All Things Root", where this type of thing is discussed. If you visit that section for your device you may find more information about this.
Please note though that while many devices have bootloaders which can be unlocked, allowing the user to modify other parts of the phone, modifying the bootloader itself is risky, since an error can leave you with a non-functional phone and no way of fixing it (since you need the bootloader to load the fixes). So you should not attempt this unless you really do know what you are doing.