Miroslav > It shouldn't affect your theme - unless of course your theme is TwentyTen, TwentyEleven, TwentyTwelve, TwentyThirteen or TwentyFourteen (I just noticed I had all 5 of them in my theme folder). If you're using a completely different theme other than the WordPress defaults, or you're using a child theme of the defaults, then you should be fine as far as your modifications go.