Can I Use TIP42 as Q1?
The SK100 is a small signal PNP transistor 1A maximum, with a small base current maximum (tens of milliamps). The TIP42 is a high current power pnp transistor, with a base current up to 1A. They are not interchangeable. 

Update: OP has provided more information, as they actually need to increase the amount of current the circuit can provide.

In this case, it should be enough to simply add the TIP42 in a darlington pair configuration. The SK100 would stay, and be used to turn on the TIP42. Disconnect the SK100's Emitter, and connect it to the TIP42's Base, while the TIP42's emitter goes to where the SK100's Emitter was. The Collector of both transistors should be connected.







simulate this circuit &ndash; Schematic created using CircuitLab

You might have to adjust R1 to provide a better total gain, if 1k is the real value of it.