This depends on the wording in the lease, which may (a) permit the tenant to make some alterations even without the landlord’s consent (b) permit the tenant to make certain alterations but only with the landlord’s consent, and (c) completely prohibit some alterations. For example, a FRI lease will typically allow a tenant to install demountable partitioning inside the property without the landlord’s consent, but require the consent of the landlord, for any other internal, non-structural alteration. Additionally, the FRI lease will usually prohibit a tenant from carrying out structural alterations to the property.