No you can not, If your referring to the Ringback Tone (the Ring Tone a Caller hears when ringing another Number when in the UK and Overseas) you cannot control this, it is generated by the Telecom Exchange and is set and approved by default by the Telecoms Standard for each Country.
Some Businesses can do this by using 3rd Party VoIP and Telecoms Cloud solutions, ie, Overseas Call Centres, but the Set Up and Ongoing Cost would not be achievable for Individual Users.
If you really don't wont people to find out your UK Mobile is Overseas when they ring you the only real way of doing this is to set All Calls to Immediate Divert to Voice Mail, then rely on VM Notification and or Dial into VM from Abroad, or tell people your only available on WhatsApp during your Overseas period.
