For transaction 'PPOME' we need to add a push button on the 'Detail Screen' for 'Positions'. But there is no 'User Exit' or BADI to do screen modifications. What should I do?
Not sure why you want to do that but you are right, there is no avenue to do it without modifying the standard program (and I would not recommend that you to do that). The standard functionality enables you to view certain position details whenever you click on one position. To view information on other infotypes, you can use menu path 'Go > Detail Object > Enhanced Object Description' after clicking on the position. Alternatively, you can configure and develop the infotypes as additional tab pages on the 'Detail' screen.