Hello,

It's not going to any problem whether you change your stream or had year gap, in many of government exam interviews are scrapped such as that of Clerk/SSC CHSL/SS CGL to name a few, in exams where interviews are conducted, you may be asked about educational background and related stuffs, but honestly speaking in any examination, the written part is the only area you've your control over in terms of performing to the best of your capability, to give you an example one of the topper in UPSC last year scored extremely good in Mains but not so good in Interview, in fact if it wasn't for his high marks in Mains, qualifying UPSC itself would have been a hurdle for him. Also, changing streams is not such a huge issue as such, many science background people have had science at 10+2 and later changed to arts stream. Always focus on your preparation part, that what matters the most in any government exams, and this is an area you have control over as I  said unlike in case of Interview.