In-place programming of ATtiny85
Yes, it is very common to put a 6-pin ISP header on your board to allow the AVR to be reprogrammed in place. Even the Arduino has one of these on it. 

Here is a nice application note from Atmel describing the typical pinout of the header along with some suggestions on how to make sure there will not be conflicts with the normal operation of the programming pins...

http://www.atmel.com/images/doc0943.pdf

If you plan on mass producing the board, you can even avoid needing the header by using this handy connector...

http://dangerousprototypes.com/2012/12/10/isptouch-header-less-isp-connector-for-avrs/

...or this one...

http://www.tag-connect.com/

Finally, you can connect directly to the chip itself using a chip clip like this ...

http://www.amazon.com/8-Pin-Gold-Plated-SOIC-Spacing/dp/B00DDE7N3C