So this would be a basic ruling one I find most annoying when my say opponent declares an a attack can he be like nah never mind ill attack someone else instead of character he originality declared an attack on

I would say as long as you've not played any "on declare" reaction cards etc. I can't see this being an issue.

Most players even in a tournament environment will be fine as long as no cards have been played

Sweet thank you so much

Also another question so say I use bossks indiscriminate fire can my opponent use there printed block on there card to block say one damage ?

It's not an attack mate so the block doesn't do anything