There are several components to gender:
1. Your biological reality (chromosomes, primary & secondary sexual characteristics)
2. Your gender identity (who you feel you are internally, even if it is a mix of the two)
3. Your preferred gender role (personality, appearance, and behavioral characteristics that are designated as masculine or feminine in your culture)
4. And loosely related, your sexual preference (same sex, opposite sex, both, or neither)
For most people, the first three components match in addition to being opposite sex attracted (but not necessarily ).
The first three components don't exactly match to varying degrees for people in this community.
Therefore, if you honor the second component (your internal gender identity) by dressing, then you are not pretending. You are presenting the way you feel you are inside (even if it fluctuates). If this does not match your biological reality (either sometimes or all the time) then you can choose to look at it one of two ways:
1. You are pretending if you call yourself a natal female (this is the way I take it that you mean)
2. Or, you can choose to identify as a crossdresser or a transwoman in which case you won't be pretending because you won't be calling yourself a natal female. This, I believe, is a more accurate way of looking at it.
Caveat: there are transwomen who cannot have SRS, yet they live and breathe full time as women just like the post-ops. In my view, these individuals deserve to call themselves women, and they are not pretending. The matter of non-matching chromosomes becomes a technical detail that the world does not need to know about (except of course their romantic partners).