transmission fluid manual says my car needs mervon v

I would insist that they change it and make it right. It needs Mercon V and nothing else. You will end up with shutter problems on take off and slippage. If you can't make them change it then get the lube guard that will change the fluid to behave like Mercon V. If it is under any kind of warranty it would be void with out the right fluid in it. Hope this helps.

Do you know how to change the oil back to mercon V and can you give me a reliable brand for mercon V?

Thanks

Well you need to drop the transmission pan to change the oil in the trans. As far as brand that isn't so important I use Valvaline but as long as it is Mercon V then that is what is most important. Now like I said you can use lubegard fluid modifier to change the fluid to perform like Mercon V. It is lubegard #62005. Here is a pic of it and yes it works. This all you would have to do is add it to the transmission and forget about it.

In the future, if i need to add transmission fluid, is that ok if I add Mercon V? You know in that case, two fluid will mix.

Yes once you use the Lubegard you can just add Merc. V as you would normally.