The term transgender / trans* has had different meanings over time. It is an umbrella term for anyone who crosses traditional gender boundaries permanently or periodically.
While it may be the case that the term transgender is and has been differently understood over time, to offer this as the ‘meaning’ of the term transgender is to provide an almost meaningless explanation.
The Gender Recognition Act of 2004 is much clearer, stating that a transgender individual:
(a) has or has had gender dysphoria,
(b) has lived in the acquired gender throughout the period of two years ending with the date on which the application is made,
(c) intends to continue to live in the acquired gender until death
This makes it plain that the condition of being transgender is permanent, not intermittent. There may be (and it appears undoubtedly are) conditions that may mean individuals intermittently identify differentially and may perhaps be described as gender diverse. This is clearly not the same as making a permanent change to one’s gender. In my opinion, to conflate these differing conditions under a poorly defined ‘umbrella’ term can only create or add to confusion.
I am writing to urge you to reconsider the meaning you have assigned to the term transgender, so that this is more clearly expressed.