Specify 2 different hotspot style (ex: 2 different images) in flash devices and html5

Yes you can.
"To specify more than one style, separate the style names by pipe | characters." - https://krpano.com/docu/xml/#plugin.style%3C/a%3E

In your case you want just different URL attribute html5 and Flash you can have only one style with attribute device properly set.
https://krpano.com/docu/xml/#devicechecksforattributes or

e.g.
url.flash="path to flash image"
url.hmtl5="path to html5 image"