[Edit: Please see the comments to find out how I was fooled by my own expectations; there is little in this post except an illustration of my misreading of the manuscript]
According to NA27/28 there is a variant at the start of Mt 10:33 (οστις δ̕ αν αρνησηται ...)
1) text οστις δ' αν
2) οστις δε (as in NA28; 1 2 as in NA27) B L 1424 pc
3) και οστις W
Quiz question: on the basis of the presented evidence, what do you think Codex Ephraemi rescriptus reads?
Since the images are online, we can check for ourselves:
Οστις δ απαρνησηται
When we look only at the first words it seems that C reads (2), οστις δε. But it also becomes clear that the variant unit as given in the pocket editions of NA27/28 cannot capture the full situation. The following verb has something to do with the variant οστις δ' αν. In some early Greek bookhands the Π and Ν are rather similar as the connecting line of the Ν between the two verticals can be quite horizontal. The presence or absence of αν is not unrelated to the presence / absence of απ- in the verb απαρνησηται.
So this is the full picture (ignoring variants in -ηται / -εται [L X 71 99 243 245 478*]):
1) text οστις δ' αν αρνησηται
2) οστις δε αρνησηται B L 517 1424 pc
3) οστις δ' απαρνησηται C
4) οστις δ' αν απαρνησηται Θ fam 1 fam 13 pc
One way in which these variants can be related to one another is to assume (2) is the origin, morphing into (3) under influence of the regularly occurring απαρνεομαι, whilst (1) is a scribal corruption of (3). The final reading is then a conflation between two secondary readings, namely (1) and (3). Of course other orders are feasible as well, for example those that start with taking the text (1) as the source of all the others. It is just that the patterns of corruption are less obvious in those orders.
Anyway, if we accept the boundaries of the variant as given in the pocket editions, C ought to be cited in support of the variant reading οστις δε. A line of support that looks like B C L 1424 has quite a bit of weight. The failure to mention C, however, is understandable in light of what follows. Shame that it requires so much work to understand C's omission from the apparatus.