The easiest and most secure way to modify the existing template is to copy it first.
With the copied template you can edit, try out and have fun without destroying the original.
Therefore, just copy the folder templates/<templatename> (e.g. templates/pacific) to default/mytemplate.
It´s important to edit templates/mytemplate/template.yml then.
The content of templates/mytemplate/template.yml should look like this:
templates:
mytemplate: # IMPORTANT: this is the unique_template_id
name: mytemplate # this name is shown in the backend
engine: PHP
skins: [default, dark, business, accessibility]
layouts: {default: layout.php, embed: embed.php}
application: [frontend, webtv]
mobile: false
separator: '::'
Clean the cache with ./vimp cc on the command line in your VIMP folder and then choose the new template in the backend (administration -> template)
Plugins (under the plugins/-folder) have their own template folders. You have to copy these folders, too.
Go to the plugins/ folder and search for the templates folders to copy, e.g. ocean:
# cd plugins/ # find ./ -name ocean -type d
As output you get e.g. (depending on the VIMP edition and installed extensions):
# find ./ -name ocean -type d ./stFacebookCommentsPlugin/templates/ocean ./stAlbumPlugin/templates/ocean ./stAdvertisementPlugin/templates/ocean ./stTwitterSharePlugin/templates/ocean ./stBatchUploadPlugin/templates/ocean ./stNewsletterPlugin/templates/ocean ./stFacebookLikePlugin/templates/ocean ./stPresetsPlugin/templates/ocean ./stGooglePlusButtonPlugin/templates/ocean ./stPaymentPaypalPlugin/templates/ocean ./stGoogleMapPlugin/templates/ocean ./stVimeoImportPlugin/templates/ocean ./stPaymentPlugin/templates/ocean ./stOpenIdPlugin/templates/ocean ./stYoutubeImportPlugin/templates/ocean ./stLiveStreamingPlugin/templates/ocean ./stFacebookConnectPlugin/templates/ocean
Now simply copy the folder and name it like your new template folders:
# cp -av stFacebookCommentsPlugin/templates/ocean stFacebookCommentsPlugin/templates/mytemplate