This is a difficult question, before answering, let's have an understanding on what is a stylistic device. From Wikipedia:
In literature and writing, Stylistic Elements are the use of any of a
variety of techniques to give an auxiliary meaning, idea, or feeling
to the literal or written.
As you probably already know, 您 is the polite way of addressing a second person, 你. Using Google search, I found quite a number of examples where both 你 and 您 are contained within a sentence:
- 您的孩子是否尊重你？ (Does your child respect you?)
- 您曾否上傳你創建的圖片，而不是用相機拍回來的？ (Did you ever upload pictures that are not taken from your camera?)
- 教您十招养车的秘籍让你的爱车光亮如新 (Teach you 10 ways to get your car a brand new look)
- 小心您的隐私：偷看你的QQ聊天记录 仅需300元 (Beware of your privacy: peep at your QQ chat record for just 300 dollars)
From these examples, it can be said that politeness is expressed at the earliest and once, only where necessary. I would reason that Chinese wants to be polite, but not overly polite that it may appear annoying, fake or impersonal such as this ad from Google:
您正在苦苦寻找顾客，而顾客也正在 Google 上寻找您。您可以在 Google
Also, the change in tone from 您 to 你 helps to bring back attention or focus to the subject (you, the reader). Therefore, contrary to other answers, I would argue that the mixing of 你 and 您 is indeed a stylistic device when used appropriately.
But for the specific example you have given, it seems to be just a case of imperfect writing, possibly due to the usage of a translation service. Instead of having so many "yous", I would have rewritten it like this:
只需一张空白的光盘或U盘，即可下载并安装 Ubuntu 桌面操作系统 。无论当前的操作系统是Windows 还是 Mac OS，您都可以用
Ubuntu 取代，或让 Ubuntu 与它共存。