A lot of landlords do not allow tenants to decorate or renovate their property. This is because some changes would only be suitable for the one particular tenant and the property may be left in a mess after the tenancy period. Some tenancy agreements allow decorations or renovations to a specified limit. These things can be negotiated though, and the landlord and the tenant may come to an agreement on what can be done and what cannot be done on the property.
Some other tenancy agreements allow for decorations to be done but require that the property is left in the same condition in which it was found. This would mean covering drilled holes, and the removal or replacement of certain fixtures and installations and more.
It is important to read and discuss the options available in the tenancy agreement in detail before embarking on any decoration or renovation projects.