What is the ruling on breaking and modifying a program for personal use, given that the company allows its use, but not fully or for a specific period? And in this case, is hacking permissible or forbidden?

The company that produced the software has intellectual property rights. If it permits its use for a specific period, then it is not permissible to circumvent this by using it afterwards without their permission, because this constitutes an infringement on the property of others.