If I add canonical tag on the pages with duplicate content pages, can I remove the tag after I get the content issue fixed? Will that have any negative effects to those pages that had the tag implemented?
No. I would advise doing this.
My other question is , in order to make the page content different on every sub category pages do you guys think I can randomize my product displays along with the text content. Does the product display counted as part of the text content?
When you say randomize, what do you actually mean?
Displaying the same products in a random order would not count as unique content.
Yes the product display does count as part of the pages content.
I'm also not sure what you mean by randomizing text content, but it sounds like a bad idea as the whole idea is to create useful unique content to the product the page is related to, which is why I suggested targeting things like "urethane body kits" rather than Lexus urethane body kits as its more likely you can produce higher quality content on the former.
hope that helps,
Woody