I think that both statements are acceptable although personally I would use 'observe' rather than recognise in this context. 'Observe' means that you are 'watching' someone/something attentively* while 'recognise' means that you identify something/someone that you have encountered before. *observe has other definitions too but I only make reference to the definition as used in the context of your sentence. Hope that helps!

Yes, there is a difference. These two verbs do not have the same meaning. 'Have you observed any changes?' = 'Have you noticed any changes?' 'Observe' means to see, often as a result of careful watching - bemerken in German. 'Recognise' has a different meaning. When you recognise someone or something, you realise that you have seen them before - erkennen in German. For example: 'Even though I hadn't seen Joan for 20 years, I recognised her immediately'. It wouldn't be normal to say "Have you recognised any changes lately?". If a native English speaker said this, I would be a little confused. If a non-native speaker said this, I would presume that they were making a mistake and using the wrong word. The correct verb here is 'observed' or 'noticed'.