  We investigate how long-range scalar interactions affect the properties of
dark matter haloes. For doing so we employ the ReBEL model which implements an
additional interaction between dark matter particles. On the phenomenological
level this is equivalent to a modification of gravity. We analyse the
differences between five ReBEL models and $\Lambda$CDM using a series of high
resolution cosmological simulations. Emphasis is placed on investigating how
halo properties change in the presence of a fifth force. We report that the
density profile of ReBEL haloes is well described by the NFW profile but with
mean concentrations from $5\%$ to a few times higher than the standard
$\Lambda$CDM value. We also find a slight increase of the halo spin for haloes
more massive than $5\times10^{11}\M_{\odot}$, reflecting a higher rotational
support of those haloes due to scalar forces. In addition, the dark matter
haloes in our models are more spherical than their counterparts in
$\Lambda$CDM. The ReBEL haloes are also more virialised, with a large
difference from $\Lambda$CDM for strong fifth forces and a much smaller change
for weak scalar interactions.
