This is a small note about how we can change the class attribute of body tag using typoscript.

# bodyTag
page.bodyTag >

page.bodyTagCObject = TEXT
page.bodyTagCObject.data = levelfield:-1 :, myfeildname, slide
page.bodyTagCObject.wrap = <body class="myclass_|">

Well here I am using a custom field added to pages table. If you wish to use the page id you may try using this code below:

# bodyTag
page.bodyTag >

page.bodyTagCObject = TEXT
page.bodyTagCObject.data = field:id
page.bodyTagCObject.wrap = <body class="myclass_|">

This way you may expect body tags like:
<body class="myclass_1">
<body class="myclass_2">

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