To answer your question OP, you will just have a slightly meatier setup compared to our stock. 205/45 compared to our stock 205/40 just means youll have a thicker/bigger sidewall. Spacers push your wheels out more thus resulting in a more negative offset, so if youre wondering if your new setup will clear the wheel well, then a spacer will have nothing to do with it. Unless you want to go more aggressive.
Keep in mind also that you want to be able to stay within the recommended ranges when choosing a tire size depending on your wheel size and width. Granted, some people love it meaty [no pun intended] and some have it stretched to clear fitment, but it doesnt mean that it is functional. Selecting the wrong tires will tremedously effect your speedometer and performance. You want to stay within the 3% range whether positive or negative on the speedo reads so youre not that off when the radar hits you. This also applies to tire performance as well.
If you wanna see what tires look like on specific sized wheels just check out tyrestretch.com to get an idea, and if you ned to calculate tire fitment so it stays within the ranges without throwing off your speedo too much, you can google 1010tires.com or willtheyfit.com
Good Luck and hope this helped.