Setting parameters to 0

Hello,

Is there a function like constpar (mixed logit package) that allows me to
set a parameter result to 0?

For example, if i have the following linear mixed effects model:

 trips ~ (var1) + (var2) + (1+var3|season)

And my var3 is "Snow Fall". I would like to set the parameter equal to 0
during the summer season. Is that possible?

Thank you for your time.

Regards,

Wafic