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Plausible deniability in cryptography allows users to deny their participation in a particular communication or the contents of their messages, thereby ensuring privacy. Popular end-to-end encrypted messaging apps employ the Signal protocol, which incorporates message deniability. However, their current user interfaces only allow access to the blunt tool of message deletion. Denying a message requires users to claim that the counterpart in their conversation has the technical sophistication to forge a message when no usable message forgery tools are available. We evaluate a step towards bridging this gap in the form of a new transcript-editing feature implemented within the Signal app which allows each user to maintain an independent, locally-editable transcript of their conversation. We gave users hands-on experience with this app in the context of resolving a social dispute, and measured their ability to understand its implications both technically and ethically. Users find our interface intuitive and can reason about deniability, but are divided by which circumstances for which deniability is appropriate or desirable. We recommend users be given transparent access to choose when their conversations are deniable versus non-repudiable, instead of the status quo of somewhere-in-between. Our study introduces a novel approach by providing hands-on experience and evaluating its usability. This method offers insights into practical deniability implementation and lays the groundwork for future research.