How can I get my iPhone 4s fixed after a screen shatter then fix?

Question

Watned to give my iPhone to my sistser for christmas because my parents said they'd get me a different iPhone 4s if i gave her my used one, but i dont want to give her a faulty phone so here's the whole story. HELP!
Purachased a iPhone 4s 16GB from Orange in the U.K in January.
Sometimes the back light goes and my screen goes dark as if it's on the lowest brightness setting! But when I go into the brightness & wallpaper tab it's on full so i just bring it down and up and its fine again for a week or so then does it again randomly!
My back screen cracked due to me dropping it (still worked not the end of the world)?
Then my lock button became jammed from time to time (not sure if before or after i cracked the back, pretty sure was before?) and now fully stops working so I have to use the assist feature to lock my phone and take screenshots.
- Anyway, I left it as it was because I cracked the back screen I didn't think Apple would help to repair it for a good price. (First Apple product so newbie to their apparent good customer service)
So thennnn the other week my friend dropped it and shattered the front screen! couldnt use the camera and it started to literally fall off
Went into Kingston Upon Thames Apple Store and was told straight up by a member of staff standing there regardless it would cost £130 to replace the whole phone. Obviously they thought I smashed the whole thing and wanted a new one, but actually I just want it replaced on account of the lock button and brightness issue which is still an issue and happened BEFORE the smash but I was too stupid to ask for help.
So today I got the front and back screen replaced on the high street for £60. Half the Apple price but it works.
BUT I didn't pay the guy to fix the lock button and brightness issue as I'm short on cash atm and think he'd mess it up some how...
So I'm guessing the third-party fix voids my warranty? Fair enough.
But if I take it back to Apple on account of I want them to repair my lock button and brightness issue, will they just replace the whole thing?
I've booked a appointment for December 4th (nearest app -_-) and in the description it asks for when booking I just said the lock button and back screen is not working.
I won't mention the high street fix BUT If they notice I've replaced the front and back screen I'll confess and say yes" I want it to be a christmas present to my sister but couldn't afford to get it fixed with you." 
Do you think they'll just charge me to fix the lock button or do a goodwill gesture or something and do the whole thing like they would of before i shattered the front screen? even though i got third party screens on it?
Really would prefer a whole new handset, this back light and lock button issue is really annoying and I know they won't believe that it happened before the phone shattered :(! They may be able to fix the lock button but the backlight? theyll probably think it happened because of the drop but it was before.
Any help, advice, or previous experiences with this issue would be great! Thankyou.

Answer 1

Kline25 wrote:
So even if I just ask to pay them to replace the lock button they won't because my screens are third-party?
Apple does not repair devices beyond replacing the screen on some models or a battery replacement.  They replace the ENTIRE device.
For the Out of Warranty replacement cost, you could have gotten a fully functional replacement device.  Instead you chose to spend less to get only the screen replaced and continue to live with additional issues.
Apple will not touch the device now.  They will know that it was opened elsewhere and that the replacement screen is not original.