yeah you can run high compression pistons, but first you need to find out if the compression will be raised by just swapping on the EX head. to do that you'll need to find out what the head volume of the head you currently have and the volume of the EX head, for example:(a pic I stole from somewhere way back)
notice how the y8 head has a smaller volume therefore it'll result in a higher compression just with the head swap, not much but still something you'll want to consider before ordering pistons. Also you should look into whether or not pistons from earlier d series engines will fit in your 1.7ltr block(i'm almost positive they will), theyre are many OEM d series pistons that'll bump up the compression for way cheaper than aftermarket pistons.